1 is plenty.

I usually get 2 or all 3, but 2 primarily collect dust.

I also have a weakness for digital sales. I buy so many games that I will never play.

I certainly never saw it as unusual. If you like to play video games and you want to have the maximum amount at your disposal, why not? 

I've fulled embraced the flexibility in having multiple consoles as when I was a kid/teen and totally reliant on my folks' money and had school to deal with, I was only permitted one console per gen. So I went with Nintendo. Now I take advantage of the fact that I can buy whatever gaming hardware I want. 

I review games now, but even before I was, I had settled on the Xbox-Nintendo duo of consoles since '05, when the 360 came out. To me, it makes sense because it covers most of my bases - I get the quirky Nintendo stuff and their second party software (and now usually indies too) on Nintendo consoles, and the bigger blockbuster style AAA stuff, quality third party games, FPS, etc on Xbox. And from a hardware standpoint, they are very different too - with Switch, I can utilize the portible functionality, Xbox is my go-to for gaming online with friends as we can actually talk online, not to mention I can enjoy 4k gaming on my new TV.

I even have a semi-decent gaming desktop, though it's been showing its age lately and I don't want to go through the hassle/financial commitment required to upgrade the parts, though most of the stuff on PC I can just get on my Xbox One anyway. 

Hell a friend of mine has all three major consoles, plus SNES/NES Classic. Another good friend has a beast of a gaming PC + Switch + XB One. That's a big out of my price range at the moment, but for now, Switch + SNES Classic + XB One + plus a lower-mid level gaming PC is more than enough for me. 

It is curious to me, why PC and XB1? Their libraries have continued to coalesce. PC is natural to me, I think everyone needs one aside from mobile gamers.

A PS4 for 2nd/3rd party games
A Switch for 1st/2nd party games
A PC for the rest.
Perfect setup

Honestly, I rarely use the PC to game these days, especially now that it's getting more outdated. The one I have now was sort of a bridge between 360 and XB One which I got a few years back. Now I mostly just play certain indies on steam, and it's my prefered way to play RTS like Starcraft, Roller Coaster Tycoon, and games like Minecraft and Terraria where mouse keyboard setup is preferable. Used to play MMOs like Everquest 1, 2, and WoW but we're talking way back. 

With the XB line of consoles, it started as mainly my console to get Rare games on as they were one of my favorite companies awhile back aside from Nintendo. Then got really into Gears, Halo to an extent, etc.. And just kinda never looked back from there. I still prefer the setup of home console gaming as a whole over PC gaming (sitting on a couch, joystick/controller, big TV, etc, vs hunched over a computer screen). XB One is my go to for modern third party games.

Was never much into Sony's brand of more linear, cinematic focused gaming. 

I would say that these days it's unusual to own only one console if you consider yourself a serious gamer.

Don't forget that we are in a bubble of a gaming forum... we aren't the norm.

The majority of gamers is probably happy with the content for their system and doesn't feel the need to buy a second system to get access to more games.