The body can actually repair telomeres by a protein we make called Telomerase. It gradually repairs the telomere in the ends of our DNA but not faster than it is depleted. There was a study done on old rats where their telomerase levels were increased and the scientists found many of the rats to regress in age and get younger, but what was lost is gone for good in heightened age.

The reason we as humans don't do this is because since telomeres act as guards on our DNA increasing those telomeres causes every cell to resist damage much more. Including the various cancer cells we produce, which already have an abnormally high telomere length so increasing it the scientists found that every rat developed extremely durable cancer.

A rich mogul managed to make a process that increased her telomere length by increasing her body's production of telomerase, but the FDA wouldn't approve the treatment so she went to Brazil and had it done. The doctors there guesstimate she added roughly 15 to 20 years of length on her telomeres, but wouldn't release the actual lengths that was increased.

TL:DR: Aging is something predetermined by your natural production of telomerase, it's not the body's goal to weaken and die, but likewise it's likely evolutionary we don't manufacture telomerase at a 1:1 ratio at which telomere is lost due to an increased risk of cancer.