And the sponsored time bought from variety steamers pretty much proves the effectiveness. It wouldn't continue happening if it wasn't worth it for the distributors. Since the links published during the stream are attributable to the source, they get a good signal that it pays off.
(+ Personal anecdote: I bought some games just because I saw them on Twitch)
https://www.reddit.com/r/gaming/comments/12zdtv1/3_years_ago...
I don’t know other way to learn about new games if not by a streamer or promoted on steam home page, steam has an awful algorithm, so you wouldn’t be recommended a lot of new games, just the same games most of the time.
For example, if you are borderline about investing in DCS (combat flightsim) and related gear, watching someone like Growling Sidewinder can tip you over. It hasn't convinced me yet because I don't wish to buy the required rig, but it might.
And I bought Il-2 after watching another channel's gameplay videos.