The reason my neighbors switched from BCBS PPO to Kaiser HMO was because their primary care MDs would retire or leave and not transfer their care and they got tired of hunting for new primary care MDs.
It has been a bit of a challenge but so far I and my extended family have always managed to obtain good to great MDs, even when our original MDs retire. We like our BCBS PPO. With Medicare A+B and insurance we rarely have any copays.
Frequent turnover is very frustrating and not a good way to get consistently good care.