One big reason that I've not replaced mine is that pretty much all current boots are a usability disaster, and a long way from comfortable. Show me a current pair of boots that remembers all my settings, that I can put on and do up in under 3 seconds, that doesn't require unreasonable exertion to get on and off (e.g. can be done by children), that is comfortable to walk in, offers variable flex (without having to take them off to change it), yet provides perfectly adequate performance (I'm not asking for miracles!). Some of these things are not important to some people (e.g. racers), but that's not the bulk of the market, including me. Performance is great, but it's not much use if it comes at the expense of comfort, practicality, usability and plain pleasure (not to mention cost).
I spent today at a big ski sale and tried on around 40 pairs of new and used boots; every pair was a struggle to get on, had fiddly, difficult adjustments, sizing all over the place - I tried 42s that I rattled in, 45s that were too small - and not one pair was remotely comfortable (and I don't have weird feet). I've had similar experiences in a boot shop trying new boots - and I've seen my friends, wife and daughter do the same. It should be better than this. Like sibhusky, I dread having to change boots, because I know that it's going to be annoyingly difficult, time-consuming, uncomfortable and expensive no matter what I do.
Some of the concepts that appeared in rear-entry boots were great, but some implementations of them were very bad, and many mistake one for the other. It doesn't help that Salomon is sitting on a bunch of relevant patents and blocking innovation. It's like they're all trying to find ways of improving the steam engine instead of inventing a new engine. While I'm waiting I'll retain an affection for my 3-second boots.