Because one day, it's how we'll all play games... one day.
Why spend thousands on PC gear or £450 on a PS5? Over the life of a console, it's cheaper to "rent", always up to date, instant access no matter where you are, instant resume, instantly swap a game, games look amazing (bandwidth depending), and they look amazing on a potato.
It's the future, and they're all trying to jump on the bandwagon.
The way we buy games is being eroded thanks to digital downloads, so why not do the same with hardware?