Why?
It is not a closed meeting.
Having someone watch the door is wise but locking the door would not keep attackers out. It is not a bank vault.
Why? Cause it makes sense. How does an attacker get through a locked door w/o alerting a security team who then respond to any threat for which they’ve been trained, active shooter scenario included. It’s not an open meeting, it’s a meeting on private property where all are welcome and a well trained security team size up unfamiliar people, or those who’ve been asked not to attend in the past (that happens) for strange behavior. Are you new to this topic?