Sharknado got busted by IATSE because they were filming the whole fuckin' thing in LA as a non-union, non-SAG production. So they agreed that Sharknado would be full union pop.
Then they started filming Sharknado 2 in secret and IATSE struck them. The production company and actors jetted to I think first Florida and then like Alabama while abandoning all the technical crew.
Subsequent Sharknado movies have been made far beyond the reach of any reasonable technicians because they've got injunctions against them and shit.
It's understandible; they're passion projects created for a tiny little indie distribution company that only has $28 billion in revenue every year.