For the same reasons I like editors that use less RAM. I leave all kinds of stuff open all the time because that's more convenient, meaning eventually I run out of RAM no matter how much I have. If an editor takes a gigabyte of ram, that means it's one of the first things I'll close because it's the largest gain. If instead the same editor would only use 100mb of ram, it could stay open indefinitely and I would close a few browser tabs instead.