Originally Posted by conspiratemus1

True, but the plastic liner wears away only until it wears through, and the cable is now rubbing against the steel helix of the housing, like before lined housing was a thing. If this introduces too much friction, especially with fragments and shreds of liner floating around in there, it will show in the shifting and then that section of housing can be replaced. The section carrying the big bend of cable to the rear derailer is likely the only section that will likely need replacing and is the easiest to replace, not being under tape. But if shifting is fine, why replace any housing?

It’s a shame that the OP is replacing cables just because the ends have frayed, (although at 6 years it’s better to start a long trip with new cables.). Using end caps would have allowed the old cables to be saved as spares.