So why aren't they handing them over to the Feds instead?
Because there's no way those packages aren't traveling between states, which makes interfering with their delivery a federal level crime.
What they don't mention.
https://losangeles.cbslocal.com/2021/07/17/after-3-separate-venue-cancellations-america-first-rally-organizers-hold-impromptu-rally-at-riverside-city-hall/
Of course they will, which is part of why it's completely meaningless and nothing more then political theater like so much else politicians say and do.
What they did is perfectly legal and constitutional.
But it's also meaningless, because all it actually means is that various politicians can't take all expenses paid trips to those states.