"Those who can't do, teach"<quoted text>
There are no laws in effect which govern the duration or proportion of hours anyone is expected to work within a given work week. Laws only exists which define a minimum level of compensation depending on the number of hours worked.
You can cry all you want about the "few hours" you perceive the average teacher tends to work, but there is nothing morally or legally wrong with them working those hours.
Before you start pointing at imaginary monkeys on other people's backs, you should take care of the real one you have on yours, created by your own aversion to the teaching profession.
George Bernard Shaw (1903)