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.
The airlines are incentivised to make it complicated, and just dealing with n different website layouts is challenging enough. Compare to e.g. food labelling, where we require mass in specific units and nutritional information in a specific format, or cars, which are obliged to include mpg and safety information from particular standardised tests in their advertising.
> And there's nothing to say that the standard bundle will necessarily meet that many people's preferences.
It doesn't have to - the point is just to have a point of comparison to be able to compare equivalent offerings from Airline A and Airline B, even if you end up getting a very different bundle from the standard one.