I agree. And wasn't the pilots suit over the Max the exact same thing? They did the same before the Max ever arrived also.By filing for an injunction or temporary restraining order now, it can prevent harm to future customers who would be buying tickets on these yet to be sold flights.
If AMFA waits, it sets up the company to get a judge to side with them to prevent the harm to those future customers.
Just ask yourself why is Delta still at Love Field?
Same reason.