I'll wrap up my thoughts on this matter:
Just as the 55 MPH federal speed limit was unworkable (and eventually rescinded in 1987), the "no saving a seat" rule is equally unworkable for the many reasons listed here. Just saying "obey the rule" can''t overcome the strong incentives to violate it, no matter how much anyone wishes that everyone will comply.
Even FIRST sees that its unworkable. Otherwise, why would FIRST tolerate teams camping out at 4 am and allow those teams to move under the eaves in the rain? Why would FIRST fail to tell volunteers to go around and warn teams not to stake out spaces at 7 am after the doors open? Why doesn't FIRST tell all teams to take all of their equipment and belongings outside during the 2 hour lunch break? The answer is obvious--they really don't care about this rule.
That said, FIRST won't change this rule until the value is readily evident to FIRST of assigning seats in some fashion. Creating an assignment system would have costs at least in volunteer time if not in materials and other resources also. It's an axiom of resolving a tragedy of the commons that the value of defining property rights need to exceed the
transaction costs of defining those rights before those rights will be defined. We probably haven't reached that point yet. There isn't enough conflict in the stands, nor embarrassing incidents with prospective sponsors. We will have to go along with teams maintaining an uneasy truce over the need to save seats for many practical reasons versus teams and spectators that may not understand those reasons.