If it was never stated that they'd get a steam key for being an early supporter, then y'all really need to let it go. But if they said they'd give steam keys for being one, but didn't, y'all have a right to be angry.
Devs require money to continue development, especially as their game continues gaining traction. Giving out steam keys would have been detrimental to the dev, as the game gained traction VERY quickly before its steam release. Blame the content creators, not the dev.