They don't want to get shot by someone from the other party.This is so backwards. You would think they would be trying to add themselves to LEOSA, not take away their own ability to have a weapon
Having the detector at the entrance shows that the major threat comes from people inside that room.
Of course if nobody is armed inside they can't defend themselves when an armed crowd shows up from the outside.
Like we saw last week.
I guess they decided it's most likely they would get harmed by a fellow congress person.