Having been on the mountains in and around Lake George (and even to the actual cave which was Cooper's inspiration for the cave in the book) I'm not going to agree that there is no where suitable. But it was likely easier to find locations in North Carolina. Still, all those rhododendrons made me laugh. I'm sure being able to pay workers less was a part of what moved film making to a wider variety of states, though the biggest influence was probably the huge tax breaks offered to film companies. Still, both California and New York are popular shooting sites. As noted by several folks above, most viewers don't know what the vegetation should be and are happy to accept what's on the screen as realistic.