Oh, it is possible that the damage is chemical rather than UV. Ours appeared first in areas where we did laundry on deck and I suspect the detergent helped its demise. But now it's starting to appear everywhere.
Some teak treatment (refreshers, brighteners, cleaners, etc.) products are also notoriously bad for the caulking (and the teak), especially if not rinsed off in the prescribed timeframe or used in hot sun, which the instructions advise against.