Its easy. Knicks havent had a legit homegrown franchise player since Ewing. Lots of fans werent even born when he was playing. KP is the next big thing, he's young, Melo (in PT) is old, out with the old, in with the new, etc...
It doesnt help that Melo has spent the last few years battling serious injuries, his stats in the 4th as far as hitting the game winning shot have been poor, but they seem better lately. Don't know how accurate that is.
Im not suggesting this is entirely fair, but its normal for a fan to want to see a potential superstar take control of the team sooner rather than later considering how bad this team has been for so long.
KP has shown that he isnt physically ready yet to be the team's closer, night in and night out. Melo still can be. Its not like KP's passing out from exhaustion, but his legs too often this season aren't there in the 4th when he needs them. At the same time KP should get featured often, wether or not someone wants to call it his team or not.