On the baggage fee:

If AA or UA charge $300 RT for a ticket from X to Y, plus the $30 RT baggage fee - then they are getting $330 RT for the ticket. Say 50% of the people check a bag - then this is a huge increase in revenue for all the flights they fly in a day.

If CO has a competitive fare of $300, but no baggage fee - then CO is only getting $300 RT for the ticket.

This is sort of like when an airline raises ticket prices $10 others match, and when some do not match they have to roll back. Basically the majors up'ed the ticket prices by $30 RT for most - and CO needs to raise as well. If AA and UA roll back the baggage fee - so will CO.