It's all about the bend radius, you can either use a similar but smaller* cable or find a more flexible one. The good ones have many fine strands twisted into small bunches which are then twisted together again, which is good for flexibility but doesn't make for slippery sliding - the multitwist cables like 7×7 can't be polished like those with 1×19 or similar construction. As with so many things, it's a compromise between performance, cost and durability. The best thing is to keep your cables clean and lubricated and well routed, and your derailleurs well adjusted and lubricated. Either replace cables on a schedule, perhaps every Easter, or as soon as you see a strand out of place during your frequent checks.


*recommended minimum bend radius is often expressed as a multiple of cable diameter, and generally ignored in the design of bike parts