Any reason why most bike derailleur cable runs, and some rear brake ones, are not set up to use continuous housing runs from the control levers to the derailleurs/brakes? Seems like with modern lined low friction and anti compression cable housings the cables would be better protected from dirt, mud and water intrusion. I would expect the added weight would be minimal, the only reason I can see for not doing so.

Most current gear hubs are set up for continuous cable housing runs as are my Avid mechanical discs.

Two reasons for it:

-weight reduction (must shave off a good 1.5g!)
-performance. Since the two cable stops on each side of the gap are immovable, there is no slop or flex in that segment, whereas there is always a smidge of slop inside a housing. And no friction in there. I think this might be a significant enough factor to be worthy of consideration.

and the real, third, reason: all bikes have to do it because that is what the top climbers in the TdF put on their bikes.

jim

I am a fan of using continuous housing... even if that means doing a little retrofitting like drilling out cable guides.

Not a bad idea from my POV. This past summer I hopped on my mountain bike to go for a 30-miler, and discovered I could not shift the front derailleur. After putting so much force into the twist grip I was afraid something would break, the cable finally broke free.

The problem turned out to be the maltodextrin/fructose solution I was using on a long mountain ride a few days before. It had dripped off the rear bottle, run down into the BB cable guide, then dried, gluing the cable into the guide.

Crisper shift of the RD, less housing "slop".