Why Start from Scratch?

I just that thought I would address this question before I get asked it, and also to remind myself when I get stuck or something.

With all the new and easy to use game engines out these like Unity, UDK, and XNA, why would anyone in their right mind want to start a game from scratch? The answer that that question, for me at least, is a little more complex then you would expect. The simple way to explain it would be to say that I just want to prove that I can, and I have a small attention span, but there are quite a few more reasons. The problem with me is that I can never stick to a decision, in an MMO I would never get to the max level because I'm always changing my class, and this part of my personality shows in my game programming. About a year ago I had this great idea to start developing iPhone games so I saved up for a Mac and by the time I finally purchased it my attention was focused on developing Xbox Indie games, by the time I made any progress on an Xbox game, I found the Unity engine. the constant back and forth made it impossible for me to make any real progress on a game.

Now I do realize that this doesn't make any sense at all, if my problem is a short attention span, why would I start a major time consuming project? Well that's where my crazy logic comes in. See, the idea is that if I develop for PC my project will be able to reach more people, not everybody has an Xbox or an iPhone so it wouldn't make too much sense to develop for those, at least in my opinion. Also since DirectX isn't hmm how do I put this... "restricted", I can do whatever I want without having to pay anything or sign some sort of contract telling me what I can and can't do.

I guess that's about it. Sorry for my terrible explanations, I'll probably expand on this later as I'm writing it really tired.