Teaching is a brutal job.
Parents complaining about grades and/or teachers. Student behaviour worse than its ever been (with administrators that do very little about it -- partly because of outside pressures). Every bit of interaction with parents, and observed problem behaviours with students, must be documented. Dates, times, what was discussed, what actions are to be taken.
Far too regular class interruptions for all sorts of things (ex. sporting events, pep rallys, dances, early dismissals, awards ceremonies, field trips, plays). Teaching gets much more difficult when a non-trivial percentage of students are out every day, and/or class time is cut short (or gone) for other activities.
Rubrics required for everything (a teacher can't just say, "this is C work" -- everything must be documented, and this makes the amount of grading work go through the roof).
Unending meetings, data collection requirements (you'd be amazed at how badly administrators want to put a number on your kids). State curriculum requirements. Standardized testing. Paperwork up the wazoo.
And I don't even need to mention that you better not need to go to the bathroom during class, because you can't leave students unattended. And between classes, well, you've got 4 minutes between bells. Better make it quick. And hope another teacher's not using the same bathroom you're heading for.
Higher pay for teachers would be nice, but that ain't the problem.