What factors led to the extinction of the trilobites?

There is no clear evidence to the extinction of the trilobites. However recent studies have shown regressive events in the early Cambrian period in the biOStratifigraphic by the severe disruption in shallow water benthos in the biotic diversity by the fine alteration of clay and organic rich laminae calcite enriched by pyrite and elements typical of anoxic conditions of water.

The failure in the symbiotic relation with parasites is also a factor to extinction of the trilobites.

Just one final note:

The trilobites were extinct only in the largest mass extinction, in the end of the Permian period.