1. Exclusives. Nintendo and Sony will never put their mainline exclusives on the PC. Flower, and Journey are ages old games, and Indies type games to boot. Them coming to PSNow means nothing. If you take Nintendo and Sony's games out of the equation you are left with half as many good AAA games to buy/play every year. You wind up missing out on the best games every year. Even if you make a PC your main platform for gaming a PS4 or Switch to supplement your options is a must. People that only own a single platform have no idea what they are talking about when they say "my platform is the best".
2. Many games get delayed on PC by six months to a year or more. I'd rather be able to play the game day 1.
3. Compatible from the start of the gen to the end. I still remember people claiming you could build a $400 PC, that ran better than a PS4 back in 2013. Well those $400 towers would now need to be upgraded just to meet minimum system requirements to run games that the base model PS4 can still run.
4. Physical games, and a right to own what you buy. I still only pay $35 to $45 for my physical games on day one. Compare that to the $60 price tag of a digital-only version of a game sold on Steam. IMO the Steam version is a blatant rip-off.
Now don't get me wrong though. I still like my PC a lot. PC has advantages of its own such as...
1. Cheaper Indie games. Indie games get released to it sooner. Many indies that come to PC will be half as much or even less than the console version. Many Indie games come to PC, and then slowly make their way to consoles months or years later.
2. Hardware that will never die, and is 100% backwards compatible.
3. PC also has good exclusives. Sure, they are a bit fewer, but PC has almost as many good AAA exclusives from 2013 to 2019 as PS4. Almost. I've lost track, but I think the current count is 25 PS4 exclusives to 10 to 15 (depending if you count expansions) good PC exclusives.
4. If you have the money, building your own PC to max settings is a lot of fun. Watching Civ 6 run with blazing fast turn times was hilarious and great!