Depends on the streamer, I guess. Personality probably matters more to those that are variety streamers - people that play many different games at any given point with a large general audience and probably less important for those that specialize in a specific game that has a built-in community of people interested in that game.
One of the finer points of something new is getting in at the right time. I have to imagine if you’re a streamer and you force yourself to stay on your old game “for the fans,” you could miss out on the shiny new thing that people care about. This could literally cost them money that they need for rent. I am confident that many streamers are not highly paid and depend on this income.
Don’t forget, fans are fickle, corporations are fickle, everyone is fickle. I don’t think any employee of a company should be loyal to that company if it is to their own detriment as that company will let their employees go if it needs to (better companies try harder, worse companies make worse decisions).
I don’t see why a streamer should treat their career differently. Do what you think is best for you. Streamers don’t owe me, the fan, and it doesn’t do me any good for them to force themselves to play a game they’re less interested in just to appease me.
Yeah, being a variety streamer is among the toughest you can be, and I’ve heard more than one streamer off-the-record complain about being “stuck in their rut” as their fan base is largely tied to a game they’re no longer passionate about.
With all the hype surrounding a Valve game, I’m not at all surprised at people jumping at the chance.