I've got so much shit to play already that I hardly ever buy games individually these days. Bundles are pretty much my main source of new games since they look like too much of a bargain to pass up. Giana Sisters is the only thing I already have from this one.
That probably much makes me scum in terms of supporting the industry.
They'd get nothing from you otherwise, now they're getting something. There's a lot of people like this, which is why they gain even as they get less per individual.
Plus it's effectively an inverse marketing budget. Especially if the game has already been out for a while.
A lot of Bundle Stars' bundles, for example, are basically games that are well past their ever selling even in Steam Sales date or would never even be noticed as existing, so they package them all up and get fifty cents or a buck per sale instead of the nothing they have been getting from those titles. Might get you just enough cash flow to get out your next title, which could possibly be more well known or even anticipated.