Complex sentence: Historically, many Pectoral Crosses were (and often still are) reliquaries with supposed fragments of the True Cross, though this was by no means universal, because of the obvious lack of enough fragments of this relic.
Split into simpler sentences: Historically, many Pectoral Crosses were (and often still are) reliquaries with fragments of the True Cross. This was by no means universal, because of the obvious lack of enough fragments of this relic.