This is because quite often the quality of the rubber used by the manufacturer, in his words are "if you wouldn't buy cheap tyres you should take this in to consideration when putting all your trust in the bit of rubber holding you up".
Linic Products Ferrule for Walking Stick, etc 22mm (7/8") BLUE X 1. L0003-B1
Linic Products Ferrule for Walking Stick, etc 22mm (7/8") LILAC X 1. L0003-L1
Linic Products Ferrule for Walking Stick, etc 19mm (3/4") LILAC X 1. L0010-L1
Linic Products Ferrule for Walking Stick, etc 19mm (3/4") RED X 1. L0010-R1
Linic Products Ferrule for Walking Stick, etc 22mm (7/8") RED X 1. L0003-R1
Linic Products Ferrule for Walking Stick, etc 19mm (3/4") GREEN X 1. L0010-GN1