Even before the TSA, airport security screening stations would occasionally refuse people other than ticketed passengers, if the load was too high (too many people waiting for the number of screening lanes, sometimes due to equipment failure). Basically, they made the decision to prioritize passengers who might miss their flights if the line got too long over non-passengers meeting arriving passengers at the gate or whatever.

The problem with that back then was that many arriving passengers expected people to be able to meet them at the gate, so they would leave the plane and wait at the gate, while the person meeting them was not allowed to go through security screening, and no announcement was made to that effect to let the arriving passenger know that the person meeting them was outside of the security screening. But that was before cell phones were common; these days, if non-passengers were allowed through, but were sometimes blocked due to high loads, the arriving passenger and person s/he is meeting can contact each other by cell phone. Buying a refundable ticket in that situation just to get through security was not a realistic option because the arriving passenger might decide to exit the secured area while the person meeting him/her was in the ticket counter line, making it even more difficult to find each other.