That's very normal for Ultrashift levers (Chorus and above 11 speed, 2009-2010 Veloce and above) where the tight 90 degree guide causes fatigue failures. I get 2500 miles out of OEM Campagnolo rear derailleur cables.

2637 miles:


New Shimano levers with under-tape routing have poor life for the same reason.

With pointy hood ergo levers the housing approaches nearly vertically and I got 4500 miles with fatigue failures nearer the head from wrapping around the shift drum.

1998-2008 rounded hood levers are also made like that but offer bar front and rear approaches for the housing.