I have a good friend who's a high level omnicrafter and is sort of a hermit. He is in a solo FC, and prefers it that way. He likes the quietness, drama free vibe of a solo FC. He also loves doing airships. Solo.
I have another friend who has a 2 person FC for her and her RL husband. They like their peace and quiet also.
There are many players like this that don't like FCs with 5, 10, 20-200 other players . Not all FCS under 4 members are up to no good. Chill and put the pitch forks down. Lol