If you're running a college and you know that the government will legislate the teachers back to work, then what motivation would you have to negotiate contracts in good faith? The employees are forced to work for you whether they agree with their employment contract or not. This is always a shitty move by the government, but it's particularly shitty when it's for non-essential services.
What you say is true of the colleges is also true of the union. And if I had paid tuition and dedicated a few years of my life to getting an education (which I did) I would most strenuously disagree with you about whether their job was essential or not. The particular issue the teachers seem to be most excised about is 'academic freedom'. I don't understand why an employee should have ANY freedom about how their job is done, let alone how they can insist upon it. You don't want to use the textbook the college wants you to use? Feel free to quit and go elsewhere.