Rent pays property tax, too. It's indirect, but it gets paid.
The older the district, the worse the financial conditions, roughly. If you rent and move to an exurb that didn't exist in 2005, they can't by definition have employees retiring from the local school in 2015 with 30 years experience and 30 years of benefits to pay out. Also roughly speaking the older the community the more corrupt it is in general, which is expensive. This is before we get into infrastructure expenses.
And it's not like the employees aren't playing into the system the same way that private sector employees pay into Social Security. Many/most state employees are excluded from participating in Social Security--the States in their infinite wisdom decided long ago that they would rather roll their own rather than submit to the tyranny of federal control.
In California, due to Proposition 13, many many landlords pay 1970's level property taxes. It makes sense to rent these properties and split the savings with the landlord.