Well, if we are to be able to sensibly compare prices between airlines without spending our whole lives reading fine print then we really need a "standard bundle" and a law that the advertised price be the price of the standard bundle. And at that point it's natural for people to want the standard bundle to match their own preferred bundle, because that will be the bundle whose price is most tightly optimized.

In the economists' world it shouldn't make any difference - a ticket for $200 plus a $20 option for a checked bag is economically equivalent to a ticket for $220 and a $20 rebate for flying without a bag, and if unbundling is really done for the passengers' sake then it will be equally worthwhile under the latter conditions. But I have a sneaking suspicion that if they had to still advertise the price as $220 then the airlines would suddenly decide it wasn't worth unbundling the checked bag after all.