Ah, the universal excuse for stealing other people's work; "free advertising".
What you are over looking is that a crappy "not as good as the paid version" game actually dilutes and damages the brand. It may advertise it, possibly, but not necessarily in a good way.
Why don't you come put a couple of weeks' work in for me? For free. But it will be excellent free advertising for your other work. The jobs where you actually get paid. I get your work for nothing, and I'll tell everyone what a great job you did and you might get paid work. Everyone wins! Then again, all you might get is more requests from tight-asses who think they can get your work for free, and the reputation you get is as "the guy who works for free". But those are the breaks.