>To provide users a way to instantly play a game without having to download all assets at once

There's a reason QuakeLive didn't catch on and it's because streaming resources to the player makes for awful UX.

>What about users who don't know how to download a model and run it locally?

Those users also don't know how to compile MS Word from source but they have been getting along just fine with installers.

The ability to paste a URL into a browser and have that be everything you need to do to play a game is pretty compelling for many kinds of games.

That’s what made flash games so big back in the day.