Perhaps they're just waiting for the complete set of fixes that will come with X3f ?

eh? perhaps they're still polishing the unicorn horns?

It's probably for the same mixture of reasons that people don't update their operating system, apply security patches to anything, never update their anti-virus definitions... Ignorance, fear, laziness, misunderstandings and sometimes plain self-defeating pig-headedness.
 
Which in turn leads to software companies installing updaters along with their products which run in the background and do their thing whether you want them to or not.

My hypothesis is that it is a result of the Sonar 8.5 resistance movement and the early issues with rolling out X1 and its new features.  There were a lot of issues with the X1 releases and, depending on what features caused a particular user grief, you could be better off staying at a lower patch level.  This was a rather disruptive period for a lot of users who found that problems (even behavior changes) could be introduced in sub-versions and the new sub-version features and functionality.
 
My experience since X2, however, has been that the sub-releases have been much better focused on addressing problems instead of changing DAW behavior.  I have made it a point to apply new patches as soon as they have been made available (from X2 on).  My advice to anyone currently is to patch early and often.  I do not recall a problem being introduced in any of the patches since X2a, but each has solved numerous problems in the main release.  This was not the case with X1.
 
Glen

Patch early and often, but backup before you do!

I think a lot of people who are afraid to patch don't have backup strategies.

I'm too lazy to update my signature.

Ah, backups and the lack of the same.
 
I once worked with someone who lost their entire Master's thesis a couple of months before the submission date thanks to a hard drive failure. Restore from a backup copy? They were "far too busy, busy, busy to have the time to waste doing backups".
 
Another lesson learned the hardest way.

Scar tissue remains the most effective teacher, for some.
 
"I was just about to backup, when......"
 
Bob Bone

I'd be more curious why anyone would still use X2. I honestly can't see why one would hesitate to update to X3e, even coming from X2, because of the sales.
 
Some may not if they're in the middle of a session and are not willing to chance losing something in the process. I'd be most concerned with that (my hard life experiences with software in general). What works can hardly be argued. What should work is not typically convincing to me.

Another reason... There are those that keep their DAW off the internet, so even an auto-notification that there's an update would never work.