Oh, come on! As a former gate lice myself, I can tell you exactly why people do this:

1) Ignorance - When you only fly a couple times a year, and you see everyone else doing it, you figure, what's wrong with it? Also, it took a while before I even realized that boarding first was a "perk" for elites. UA needs to be firmer about this, or the behavior will continue.

2) Rationality - I used to push to get on first because as long as UA (a) doesn't enforce carryon limits, (b) takes forever to offload luggage, and (c) loses bags with regularity, I'd rather piss off elites standing in line than risk having to check a bag and go without clothes for a week. Don't blame pax for what is, really, rational behavior under the circumstances.

So have a heart, and direct your fire at the airline!