Because people are still buying it with over 2m sold across all platforms. And Capcom seemingly wants every mainline RE to be available on current gen platforms.
Other folks in this thread have mentioned wanting new costumes, but you know what I would love to see in this port? The ability to use all the goofy costumes already in the game right from the get go in the campaign, without having to spend hours grinding in Raid to unlock them. I just don't want to do that shit again (I'm honestly not a big fan of Raid mode in general, really). Just let me be a sexy pirate/sailor from the beginning,
y'know?
Uh, how would you play them though? With an analogue stick? That's downright painful to do in the PS3 versions. So awkward and obviously shoehorned into something designed from the ground up for motion controls.