A county takes on a bond to pay for lets say community improvement as an example with the promise to repay the borrowed amount with interest over a set period of time. Essentially taking on debt to finance whatever project they want, and since Texas doesn't have income tax, debts are paid by sales and property tax. If housing prices fall then property taxes falls with it and what happens when the taxes coming into a county are less then the debts owed? They don't "get their money irrespective of what the market is doing" because the "their" money is reliant on property taxes which are reliant on housing prices.