> Why do people thinking teaching is any harder than any other job that requires a university education?

Because not every job that requires a university education is equally demanding. As you said, some of those office jobs are outright boring. Teaching is far from boring, but it can be incredibly draining as there are a lot of expectations to meet.

> including summer holiday

It is easy to look at this and ignore the fact that in order to teach properly, a teacher's workday isn't 9-5. It is in fact much longer and often work carries over in the weekend because papers need grading, lessons need to be prepared, etc, etc.

There is more to expand on here, but the way you dismissively phrased your comment makes me think you aren't really interested in constructive discussion about the subject.