Well, I have personally witnessed passengers stuffing the most outrageously bulky and heavy pieces of baggage into the overhead lockers in the business and first class sections of the world's so-called legacy carriers (including the likes of BA).
I really don't think this phenomena is at all unique to low cost carriers.
Perhaps it is simply that those of you out there who think that it is, have never ever managed to grace the forward sections of the so-called legacy carriers with your esteemed presence and therefore have no experience upon which to comment with any degree of accuracy?