For the same reason much of the Sony camp want Sony to buy square enix

They all want their favourite box to win

Considering all Sony has done is buy studios it already had close ties with of which all, seemingly to me, was mostly out of fear MS would buy them instead (outside of Bungie and a PC converstion specialist), I doubt it we'll see the big guns buy much more after this. MS won't be able to ever buy another publisher because that would be too much control and I'd hope regulators actually keep and eye on what smaller studios they do buy too but we will see.

On the latter, Apple and Google would have been options but there is the risk of them taking the games and putting certain ones on their mobile devices only but this wouldn't have affected console and PCs as both would have been stupid to give up that revenue. Amazon have nothing in the gaming world so

Its a good thing for few and bad thing for some, also it wont be a good or bad for most.

For those who see it as Good
-Microsoft - they would get access/ownership to a ton of IPs and games, for their main goal being Xbox Game Pass, it would make the service look more attractive and give them the advantage over competitors.
-Xbox fans - the typical console warring fan would be happy that their favorite company won
-Activision Blizzard - a new form of management would be good especially with who ABK currently has right now, leadership changes can and will occur, the way internal affairs will run could possibly change but you probably wont be able to see the results of that for a while.

For those who see it as Bad
-Sony - the fact that they would have to negotiate with a major competitor is something that they frown upon to get access to IPs such as Call of Duty. It also puts them at disadvantage even if CoD releases on Playstation due to the fact that if CoD gets day 1 release on Game Pass, its gonna be hard to sell a $70 game over paying for a service that lets you play CoD along with other games for far less and on both Xbox and PC.
-Playstation fans - the opposite of Xbox fans mentioned above

For those who are neutral or not affected by this as much (or can go either way depending on the situation)
-Nintendo - getting a Call of Duty game (s) via the negotiation deal that MS made earlier would allow them to finally get Call of Duty again.
-Valve - like Nintendo (although in a lesser way) since Call of Duty just recently started popping up again on Steam. Though the chances of a potential Diablo/Starcraft/etc releasing on Steam is higher now if the deal goes through. However its still 50/50 because like Minecraft, there's a chance we might not still see any Diablo or Starcraft game coming to Steam.
-Gamers who dont care which system a game comes out on - likely wont be affected because if its a game they want, they'll get the platform (or already have it) or they wont get the game at all if there's no interest in it to begin with.

As for me personally - I dont really care if the deal goes through or not - I have access to all the platforms whether its Playstation, Nintendo, Xbox, PC or mobile.

I dont subscribe to any game subs like NSO, Playstation Plus or GamePass/Xbox Gold - so its whatever for me.

Edit: As for Call of Duty is concerned - most of my CoD library is on Steam, the only Call of Duty game I dont have on Steam (that I havent bought already) is Call of Duty 3 and thats console exclusive - which I already have for Xbox.

One of the biggest companies buying another of the biggest companies is just bad until proven wrong, IMO.
It can end up being good, but this is business, neither MS, or Activision, or Sony, or anyone else care about doing things for it to end up good for the consumer, the very opposite, actually.
Always sad to see people applaud this, but oh well, now some other people will want Sony to go and buy Take Two or something... great...

The thing is that MS want to go the Office route with Xbox, and that’s not a route with low quality.

They will introduce different tiers for Gamepass in which you can get all games or just a few depending on the fee you pay, quality of the projects (as with any subscription service) will start to decline.

And not kid ourselves, many projects will be PC/Xbox/Switch in the future, even the Big IP’s.

Is very clear they want Sony out of the business as Sony would do the same to them if they have the opportunity.

I never cared much for Activision/Blizzard games. But getting CoD on Switch is a nice bonus.
Beyond that Activision was planning to basically have all their studios work on CoD games and nothing else. I see here a good possibility of some dormant franchises finally getting new releases after a long time. Even if I personally don't care.
Also more games coming to Gamepass and various cloud services. Again I personally don't really care, but it has a positive effect for many people.

Additionally ABK employees now get to unionize. They basically all wanted the merger to happen.

I hope you're right but I doubt it. 10 years. In 10 years I predict the landscape would be completely different. I don't see many companies giving in to acquisitions now, but with the surge in production cost and risk, I have a feeling some of them would eventually accept the offer. There's already lots of studios that did, and examples like big Football clubs owned by oil money.

I hate the whole consolidation, but since we're going that way, at this point I'd like to see some aggression from Nintendo as well. Take-Two and EA are obviously out of the question, but Koei Tecmo would be an excellent fit for Nintendo. 

Single player games can be live service too as well as designed to be as addictive as possible to retain players. But there are always exception, hence I say even more.

By less choice I mean there will be fewer publishers, thus less need to compete, resulting in less choice and lower quality overall. 3rd parties have always been a big driving force which are now slowly getting gobbled up by the platform holders. Why would Bethesda compete with ActiBlizz when they're both under the same roof? In the end fewer, more addictive games with lots of MTX results in the most profit for platform holders.

Digital killed the A/AA game market, subscriptions won't kill AAA gaming but will reduce options. No idea why people would welcome a landscape where it's just the 3 platform holders deciding on and making the games. Anyway content delivery and content creation should be separate for maximum competition and creativity. Eff a future where everything is 1st party.

Win what? The console war has been over for a while now...

Atm is more of, lemme have it for 'free' on GP or PS+ extra. Or fearing that future games won't be coming to the box they bought or subscription service they signed up for.

I guess we have the subscription wars now. VGChartz should start tracking subscription numbers rather than unit sales ;)