the cable tends to dry n stick n wear out the outer cable lining. prob inherent issue with most cable operated mechanisms under high tension loads.
I'd highly recommend taking the cable out, inject a load of wd40 through it and move the cable in/out to work the oil through till it drips out the other end and will notice it gets less sticky.
I experienced that if ignored, it could get so heavy that either the cable rivet end shears off, outer cable wears out or worse case is actually fracture the clutch pedal mount off the bulkhead.