I imagine Chase must be paying some / all of the cardmember earn rate step-up. UA may have just cut the cost of providing rewards by 40%, because they don't award it to non-cardmembers or Chase pays it for cardmembers.

I am kind of amazed that airline loyalty has now become "if you buy the cheapest fare you get no reason to come back and fly us again, you should be paying us more to engage with the loyalty program". If you watch UA flights board, there are often a number of people in Group 6 that brought a carry-on bag and end up paying $65 at the gate to gate check their carry-on. Even with that bad taste in their mouths, those basic economy customers might have had a few miles in their account that did not expire that would bring them back to try UA again in the future. Now, a bunch of new fliers are going to have MileagePlus accounts (that they signed up for to get Wi-Fi) with 0 miles in them.

I have enjoyed UA basic economy for markets like BOS-ORD because it earned full RDMs, PQPs, and million miler credit, as well as having free standby if I got to the airport early. Given the tickets are so cheap, the RDMs are not that much, and this will probably not change my behavior when UA is the cheapest option. I am probably the type of customer that UA wants to fire (or reward less), but it's still disappointing. I also wonder how this will affect crediting to B6 (and whether there may be a merger offer), since I have Mosaic 1 for the next 25 years.