I would suspect local LE, even if they had permission to fire were not in a good position for a clear shot or to even see what was exactly going on as they were likely on the ground vs the roof top USSS snipers. They may have been first to know, but the best people to observe and take action were the USSS snipers/commanding officers.
I’ve heard that those rooftop guys were local SWAT. They were the ones awaiting a go sign to engage.
DJT had a bare-bones SS detail. The good ones were called away to some spaghetti feed to cover Jill Biden, I believe.