Except there is a reason for doing it, and the airlines themselves have created/exacerbated that reason:

Not enough overhead bin space, combined with fees for checked bags. Given that, why should someone with a less fortuitous boarding zone be penalized relative to other passengers, who may well have paid less or the same for a more advantaged boarding zone which gives them preferential access to a scarce resource?

If the economically LOGICAL resource allocation was done, whereby checked bags were free, but carry-ons that only fit in the overhead bins (which, after all, are the scarce resource) were charged-for instead, this problem would go away.