Ben Gilbert/InsiderVideo game streaming is not the same as video or music streaming, and there's one clear reason for that: Interactivity.
For most players, the time it takes for a button press to translate into in-game action on a local device is imperceptible. You push A, and the little plumber leaps into the air.
But the equation changes when the internet gets involved: You push A, that button press is sent to a device in the cloud that's actually powering the game, it registers your input, and the live video of that is sent back to you. The plumber leaps once again.
That concept, known as "input lag," is key to why video game streaming isn't the same as music or video. If players feel a disconnection between their actions and the game they're playing, it could ruin the experience and/or outright render the game unplayable. It's a critical part of why, thus far, no major video game streaming service has been successful.
But with Xbox Game Pass, streaming doesn't have to be perfect — it's a value add to a service that's already a good deal. It enables subscribers to easily, immediately try a game before fully downloading it, and to do that wherever they want. If they like the game, but don't like the input lag, they can just download the game to their Xbox or PC.
The streaming element isn't intended to replace the core service, but to complement it. And it does that generously.