From my (limited) experience, novels are very different to short stories. You can hold the whole concept of a short story in your head at one time.. but novels are big and slippery. Things change and develop as you write - so you often have to go back and rewrite or even delete huge swathes of things to fit the new pattern and flow. There are some people who can do without this - but IMO they're either brilliant writing geniuses (to whom we should not compare ourselves) or they're incredibly experienced writers who started out by going through the major-overhaul process... but who have now honed their talent so much they no longer need it... leaving us still in need, generally, of rewriting.

This is not to say that maybe you're an exception - or maybe you're much better at planning (and sticking to the plan) than me :)