Because Mozilla has proven time and again to be a false friend to the foss community. Look at thunderbird and xul, not to mention the fact that they basically ended up copying chromium..
Chromium is leading the market by a wide margin in security.
Forking Chromium is the only current viable way forward.
I disable all the crypto integration and use it because it's precisely "chromium without google services but still usable", all while remaining open source and focusing on privacy, something that Edge, Vivaldi and Opera do not.
Edit: Who can afford paying a premium for privacy (if one agrees with the parent assumption, that is).