Aaarrrrrrr, why? 

A Steam game that I want to get needs a Xbox controller, and controllers are required. Why do they clearly prefer a Xbox controller when nobody even plays the Xbox?

Xbox should just give up so that the industry can move on. 

I use an Xbox 360 controller on my PC. It's been some years already.

I don't think I can go back to DualShock.

Xbox controllers tend to be the most popular controllers on PC. That is why.

Do you know how overwhelmingly used Xbox controllers are on PC? Lol like, it’s not even close.

You rarely see PlayStation or Nintendo controllers used. You’re more likely to see third party controllers with an Xbox layout than you are the other 2. That’s why Xbox puts out so many controllers. And it’s natively supported on Windows.

If you want a different layout, just go to the games properties in your Steam library and set the Steam Input to PlayStation.

Xbox 360 and on has been the standard for PC controllers.
And are they making you use an Xbox official or styled controller? Maybe I'm missing something, but I don't think they force that on Steam and other ecosystems.

I rarely play on PC but when I do I use a Series X controller. Most people use an Xbox controller.

I don't know about other controllers, but I'm pretty sure Steam supports Sony's controllers in all games that supports controllers. You might have to change some controller options for the game via Steam (not in-game!), but I'm pretty sure that way you can tell Steam to essentially mimic an Xbox controller regardless of what you're using. I recently played Pumpkin Jack using DualShock 4, and the game officially supports only Xbox controllers (support for other controllers is listed as 'not known'). The key prompts look like Xbox buttons in-game, but usually it's not really an issue.

There was a time when the 360 controller was basically the default for PC controllers and it persisted for years. That might be why they require it. They think there's a ton of Xbox controllers out there.

But I agree. This would be frustrating.

It's only relatively recently in PC-terms that Sony's controllers have support. (Think: Less than 10 years)
And it's mostly thanks to valve providing the intermediary support.

Many older games will need to use a 3rd party application like DS4Windows to trick the game into thinking it's an Xbox controller that is using Xinput.

One good thing Microsoft has done over the last several decades was its PC xbox controller support while Sony and Nintendo looked the other way... Xbox controllers are just a flawless experience... Not to mention before Microsoft came along, PC controllers were cheap junk from the like of Logitech.