I usually opt to sit and wait outside the gate until I can assume that most people have gotten to their seats inside the plane and won't crowd the aisle. The seats are assigned anyway, it's not like I'd get a better spot by being early. So why not wait outside where there's plenty of space and (usually) fresher air?
No, the only reason I can think of is that people want to make sure they have place for their oversized carry on (as the article alludes to). If that's the case I have no sympathy for them, and hope they all get stuck next to a fat person with a cold.