The true reason people don't like small player sizes: It highlights their mediocrity that much more. If you have 63 other people to shoot at, it's that much easier to perform to ego pleasing levels, since there's always someone to shoot at. It's also easier to hide your shame in the masses when you do nothing but trade kills, or worse, feed the enemy team the entire match.
This is compounded by unlock systems. Suddenly the shitty, tiny killbox map is that much more appealing and TDM is the most popular mode. Let's turn on instant re-spawn while we're at it, wouldn't want to be in a queue "half the match" because your dumb ass sprints into enemy fire all the time. Join the fish in the barrel, this is a good experience.

That said, small teams are clearly not the path to success in this shitty environment, so I agree that it could be bad for Titanfall.