Why does the government wait years to execute death row inmates?

Housing these inmates costs thousands of additional dollars to us, the taxpayers. These inmates are scheduled to be executed anyway, so why delay the process - in the meantime charging society hundreds of thousands of dollars? The estimated time a death row inmate spends in jail is 10 years before being executed. Sounds like too long to me. As for the appeals, I believe they should only get one. Sure, a few of them may be innocent, but the verdict has been sealed. Society makes mistakes. There are thousands of innocent people in jail right now, but we don't let them all out for the benefit of the doubt. They have been convicted, and they are serving the time. Likewise, there will always be a couple of innocent death row inmates, but as I said, society will ALWAYS make mistakes. Having said that, it's unnecessary and rather costly to keep thousands of inmates for a period of ten years - when they will clearly reach the same fate regardless of time.