At first, I was thinking the OP was justified in being upset over rules applied in ignorance - possible interference etc. ( which episode of the Simpsons was it were all the mechatronics in the park went on the rampage
However, on security grounds I can see it making sense:
It is such a symbolic location and families expect to be safe there.
If any disruptive group were to organise anything untowards, unmonitored comms would be valuable to them.
FRS provides a finite number of in the clear channels than can be monitored, and cellphones could be logged and location triangulated or quickly shut down.
So FRS and cellphones ok - more professional looking radios not ok - accept it and try to have a better day next time.