One of our AT forum regular members works for an airline - but that person is not lien (nor me).
All airlines have schedule changes. With the UA / CO merger that will have meant the potential for even more changes, not to mention a loss of routes and services across the airline industry in the last three or four years.
Change fees are set by the airlines, clearly posted for all to view. Changing a date or routing may incur an additional fare - again not something done by UA only, nor is it hidden, but indicated in the T&C of ticket purchase.
Lost or delayed bags are a pain in the neck, never a pleasure to have to deal with. If bags are delayed because of a schedule change then the onus is on the airline to ensure the bag is reunited with the owner in good time.
If bags are delayed because the passenger checked it at the last minute or allowed the minimum connection time at a busy airport that might be another story. The onus is still on the airline to do what it can to renunite pax and bag. Contact details inside the bag can go a long way to help this process along.