When a judge issues a legal court order and it is disobeyed or flouted, the judge has huge powers to coerce compliance.
After issuing the back to work order, the judge could jail all teachers that refused to work indefinitely, until they agreed to comply with his order, AND he can jail them for a specific period for failure to comply originally. Allowing replacement hires is a very minor punishment.
It's not wise to piss off a judge.
Every one of those teachers (well, at least the ones walking the line) are in contempt of court right now.
Having spent a couple days in jail once for contempt related to a discovery issue in a civil proceeding, I agree with everything you say.
That said, it begs the question of why isn’t the judge doing exactly that?
Likely answer: All counties all over the US are broke and locking up 1,100 people would be expensive.