The problem is distributing the game ONLY through Steam. There are people that don't like the platform, they don't have to justify themselves for this. They want to support the developpers, and the devs basically spit on their money. This is just wrong. Providing a separate download of the game does not cost money. Hell, they could just torrent it, no significant bandwidth cost for the devs. Just make it so that the game unlocks using a purchased serial code (it does not even need to connect to the web, offline validation could work) and BAM : you're providing an alternate download platform basically for free.
It is -a lot- of work to put something like this up. Especially if you are "only" a creative developer. There are plenty of legal and financial pitfalls ranging from obligations, refunds, accounting, taxes and so on. Steam takes this away from the developer so he can focus on the imporant part: game making.
You can't just "whip up a paypal account and put the game on your homepage".
And for those really having a problem with Steam, just pirate the damn game after you bought it.