I'm not entirely sure I blame the airlines entirely as these tickets often involve some time and work. If an airline isn't receiving any (or very little revenue) from the ticket their position that you should issue from one of the airlines that is to me isn't unreasonable. So if I want AA to issue I will usually put at least one intercontinental segment on AA; same rationale would apply for BA, JL, or any other airline I am asking to issue the ticket.

Was there some particular reason you couldn't add a BA segment?