They paid him as if he would pitch like his prime well into his mid 30's.
He was worth the money they paid him the year before he signed. There is no way he would be worth that by the time he hit his thirties. To think he would continue that production way into his 30's is stupid.
Typical Brian Sabean thinking.
They could get the same production for half the price--even without his injuries (which are pretty much a given over the course of the contract given the years he's pitching).