I actually don't. Amex also offers the Aspire card, which reimburses for up to $200 in airline tickets for bookings made directly with airlines (including United). And of course Chase has the popular Sapphire Reserve card, which not only reimburses for up to $300 for all direct bookings with airlines, but also for literally anything in the travel category, and this is true even for airlines that partner with Amex (such as DL). If Amex wants to make their credit harder to use on this one particular card, I don't see why Chase would particularly care. Amex still reimburses for UA tickets, not just TB purchases, on the Aspire card. And once one buys a UA ticket with the TB purchases, one still needs either UA status or a Chase UA card to avoid baggage fees.