There just isnt the money in regional airports for BA, its great to fill a 737 at £29 economy but BA's cost base needs business pax and lots of it. Only MAN/BHX/GLA and EDI really provide, and even then the latter 2 only on the standard CDG/BRU/AMS etc. It is far cheaper for Lufthansa to provide a FRA-MME/LBA service as they dont have to have expense of basing aircraft there.