You’ll notice that the 4s are all hugging the exits – it’s the most lucrative spot. Yes, you have to squeeze in when the doors open to let people in and out, but you also get to gtfo first. You’re not subject to the Showtime kids doing flips, when the Mariachi band walks in you can run out to another car at the next stop, and you aren’t in the urination/defecation areas. Sitting is a trap.
People with toddlers often keep the knobs off as a form of baby proofing, when the kiddos are tall enough to reach but not old enough to listen. It’s then easy to lose a knob that isn’t in the right place.