The recent indie release, Kitsune Tails, was available on Steam and Itch, but the creator actually made clear on social media that Steam reviews were really important and that they were only counted properly if the game was bought on Steam and not added there via a key. They were really pushing to hit Overwhelmingly Positive shortly after release, I don't know if that was the only reason, though.
Also in your advice where you recommend verifying a crack exists before buying on Steam, isn't it similar to see if a GOG (drm-free) version exists that you could fetch at no cost later if needed, and then buy on Steam?
If the game developer wants to follow a particular marketing plan, e.g. they've discovered they get more sales when there's a lot of positive Steam reviews, then of course you can help with that. If retweets, or Reddit posts, or Facebook likes or lets-play Twitch streams, or whatever else sells copies, and you're in a position to do that...
However, when buying on Steam, you need to watch out for your own interests too. Will you still be able to play this game in 20 years? Checking there is a crack is your insurance policy.
If you can buy it DRM-free on itch.io or GOG, do that instead. Steam store pages will list if there is any _third-party_ DRM, but won't list if the developer is using Steamworks DRM, so generally you have to assume it is (unless the developer assures otherwise, or it's on https://www.pcgamingwiki.com/wiki/The_big_list_of_DRM-free_g... )
Also in your advice where you recommend verifying a crack exists before buying on Steam, isn't it similar to see if a GOG (drm-free) version exists that you could fetch at no cost later if needed, and then buy on Steam?