Because we keep begging for retreads of our old favorites?
It isn't like RPGs are the only place where we see lots of remakes and sequels. I would expect the same dynamic to apply here - so long as we continue to buy based on an old name, we give them a disincentive to take risks.
Especially THIS past year...how many freaking "80s" movies got made (I'm including things like Hot Tub Time Machine and Stallone's "The Expendables").
Seriously..when the Expendables pretty much demolished a relatively fresh/new property like Scott Pilgrim vs the World, the power of nostalgia can NOT be ignored...