My reasons for not switching are pretty simple:
1. So far, everything the designers have said and shown about the new game (including the references to using Saga and 9 Swords as test beds) has been not just unappealing and uninteresting, but in many cases, contrary to how I think a game should be designed (for my tastes at least). I don't have a problem with this. They aren't designing a game for me, so it'll just be one of many games not designed for my play style.
2. I'm currently using a hacked, mauled, kit-based version of d20. So far, it's done everything I need a game to do. It still needs somw twisting here and there before I'm finished, but knowing my and my penchant for fiddling with rules, it'll never actually be done.
3. I'm not keen on what I've read about the new game license so far.
I hope those who do adopt 4E have a blast with their gaming. Unlike a lot of posters on assorted boards, I don't take the whole change as some kind of personal attack. It sounds like 4E is going to be a great game for some play styles, and that's great. Every edition is going to leave some people behind - that's just the nature of things. I dont' have a problem being behind the SOTA.