I have a theory that something else is going on with Shake Shack. There is a provision that was slipped into the Paycheck Protection Act that requires businesses that take funds to remain neutral in any union organizing effort. My bet is that Shake Shack learned about this provision and returned the money in a nanosecond.
Actually, that only applies to mid-size business loans, which is different than the the PPP loans. The mid-size business loan program is not forgivable (like the PPP loan) and the stay neutral only applies during the terms of the loan.