Shallow hardening. Poor hardening. Case hardening being worn down on a low carbon frizzen. Steel tempered too soft allowing too much metal being racked off, also too strong of a mainspring doing the same. The latter usually produces short flint lives and broken flints. A poor choice of steel by the maker. Wearing out a frizzen of a good steel with a good heat treat and the lock having a good balance in springs, is rare.
I have worn out two freezen: an Ardesa/Traditions and a Pedersoli. The reason was very simple: the steel was not hard enough and too low in carbon...
As a watchmaker, I had thin steel sheets with a lot of carbon, so I made the steel faces hardened and tempered light blue and I never had a problem with them again...
Maybe it's your or the problem you are talking about: not enough carbon or not hardened enough...