I assume it's so that if your client wants, it can reach out to a different BFF to get some data not implemented in its own BFF, leading to a class of problems

I assume it's so that if your client wants, it can reach out to a different BFF to get some data not implemented in its own BFF, leading to a class of problems where the data might change, necessitating the need to build Backend for Backend for Frontends (BFBFFs) on top of the BFFs. That way you and your competing teams can wage an arms race to see whose jenga tech silo can grow faster.