Generalizing why people aren't doing something is pretty bad form. There are a lot of reasons why not to make the switch, though I'm not going to go into them here as they've been debated to death. I wouldn't discount the large amount of gamers who don't post on the net or feel the need to give voice to their reasoning. People who aren't making the switch can get treated pretty roughly by those who are, after all.
Ultimately, you might be right about 3.5 waning in popularity, but I think comparing 3.5 to another edition is a bit like comparing apples and oranges. Sure, they're kind of similar...well, you get the idea. The point is that nobody knows what's going to happen. It might flop. It might soar. We probably won't definitely know for another 10 years, if at all.