They aren't standard working terms because of the unions. They are standard working terms because all teachers (who work in state schools at least) are employed by the local education authorities, who in turn set their working terms and salaries based on the government's department for education. So for teachers there is no individual salary negotiation, it's all decided centrally by the government and you either take it, or move to the private schools of which there are a lot less. (This is UK for me, but based on what op said, I think it's similar)

Yep very similar. There is built in some automatic compensation for years of service, and the payscale is inflation adjusted. For a given position, there is a small range of possible salaries. So it is in principle possible to have a bit of independently negotiated salary. In practice almost everyone falls very close to each-other.

This is not to say that individual teachers cannot earn more or less, just that the scale on which they are being paid has been decided in advance, right?

Percentage of revenue going to the players has already been negotiated.

It should also be noted that the players union represents a tiny portion of the actual employees involved and they actively negotiate money away from other employees.