How are conference TPC (Technical Program Committee) members selected? I've been a member of TPC (Technical Program Committee) of some famous conferences for few years. But this year, I, along with many, were not invited.

Wondering how is TPC selected? I guess the TPC chairs select those? But TPC chairs are actually the same as before!
They are selected by the conference chair to be on the technical program committee.  People on the technical committee may suggest other people.  Some times they will ask past authors of the conference to be on the committee.