Because I didn't struggle my way through an engineering degree instead of partying my way through a communications degree just to become a teacher! That's said as if it is supposed to be impressive. Assuming a half-hour lunch, 3:30 would be 8 hours. In order to work a basic 40-hour full-time job in 9 months, teachers would have to work roughly from 7 to 6 every day (10.5 hours). I won't complain about working more because I get paid for overtime, but an awful lot of people work more than 40 hours in a typical week and don't get paid overtime.
Regarding your pay data, it's way too low to be representative. In NJ, starting average is $38,000 and average average is $58,000. Both of those are top 5 in the country, though:
http://teacherportal.com/salary/New-Jersey-teacher-salary
However, given that they only work about 9 months a year, that's more like $50,000 and $77,000 a year.
I'm alo pretty sure that's just base pay - it doesn't include benefits, which are much better than in most other jobs. Not to mention near-absolute job security...