I would hazzard a guess that living the ex pat life is not on some peoples radar (or their wives). So putting up with BA and the company it has become in the 2000s for the rest of their careers, and enjoying the best flying T&Cs the UK has to offer, is the best of a bad lot.
The fact people dont want to move isnt relevent, the point is that there are comparable T+Cs around. The senior dead wood in the cabin crew community would never be able to get anywhere near the same conditions elsewhere.
I think youd be suprised how many pilots lose their job in BA through poor performance in Sims etc. Theres at least 20 ex LGW capts on the -400 in the RHS by choice.