Beyond "trying out" games. I like the idea of saving things or quickly grabbing things that might not be available for long. For example on a hard drive somewhere I have that early test build of Skate that was leaked like a year or two ago.
I'll also say that as I get older I really appreciate how many more plug-and-play resources there are now. I can get a whole game package that self installs and I'm good to go. No more having to get an ISO from some sketchy Russian site or rolling the dice on TPB and then mounting it to virtual disk. With the power of adblockers/tracking blockers I can stream basically anything from any service with a few clicks from the megathread.
I think it's plain and simple greed. Tech company executives are blind to the reality they live in, they don't see that they already have more money than God, they just see opportunities to make more money. I think everything we're seeing is an effort to milk the platform for all its worth right at the IPO then ride off into the sunset.