Well, that, and that in the story of the tax collector and the Pharisee, the tax collector “stood off at a distance.” So avoiding the place of honor is the reason for some.
There are also people who start out back there because they have small children who are prone to start screaming in the middle of Mass (or because they were that small child), have an active bladder, or have some other reason to foresee having to make a unobtrusive exit. Even when the problem resolves, it sometimes gets to be a habit for the family to be back there.
Some people feel a bit exposed to be in sight of everyone else. Some people want to leave the front seats for people who have trouble walking or people with well-behaved small children who want to be able to see. Some people just like the back better, just as people may have very different favorite seats in a movie theatre. There are lots of reasons.
Likewise, some people sit in front in order to leave the back open for those with small children, for the unobtrusive entry of those who were held up and come in late, and so on. Since the front is no longer a place of honor, one isn’t better than the other, assuming that the people who need to sit in a particular place are accomodated first.