Jeez. I mean I agree that a non-DRM version of a game trumps steam's "license" system any day, but the situation is far more complex than just DRM vs non-DRM. Pricing, availability, purchase options, exclusives, game version maintenance / features etc all play a role. For some, just being able to buy a game, play it through and move on never to play it again is enough for them, and I can understand that. For these gamers, the "evils" of using a client to dictate the game installation and usage isn't a huge concern (until it bites them on the ass of course).
In my book, encouragement of players to support GOG is fantastic! But don't demonize users here for using other storefronts as well. After all, some are buying games on sale on steam (cheaper) and if they love it, buy it on GOG to keep
them. But by all means, keep slapping that bull on the ass by posting this can of worms here.
Like many have said everyone is free to get their games from wherever they want but the point of OP is that when people keep buying products on a platform they support that platform. As long as they get (enough) money they will just continue with what they're doing, and (some) game devs/publishers will continue to release exclusive content on that platform.
The thing is if enough people really do care about DRM free games and decide not to buy and so not support x platform even if that means not being able to play x game, devs/publishers will start to think if it may be better to just/also release their games in other places.
I truly believe If enough people already had done that, even more games that are still exclusive on x platform would already been released here on GOG and DRM-free, but nobody can't tell people just where to buy and what to buy, people will decide for themselves what they believe is best.