The problem is that it is very hard to find band sizes that fit their man chests. Only land whales need those large band sizes. Even if you can, at those sizes (40 and up), they assume if you are that fat, you must have big breasts. So, those will generally start at a C cup instead of the AA or A that most moobs would need. That's also why it is hard for a slim woman with large breasts to find a good fitting bra. If you need a 32 DDD, it will be slim pickings. Most DDD start at 36.
I'm honestly surprised more of them don't go to Victoria's secret and get fitted properly for a bra. Seems like that would be very gender euphoric. Especially making the young women who work there look at your moobs and measure them. If they had any clue about bras, more of them would do it, I bet.