They fail due to fatigue so it depends on how much you shift.

I ride tight cassettes (13-14-15-16-17-18-19-21 in the 8 cog era, 13-23 9, 13-26 or 14-23 straight block 10) and shift like I have ADHD for a metronomic cadence.

Typical right cable life was 4000-4500 miles for me with pointy-hood Campagnolo ergo levers with most of the bend in the cable housing; Ulrashift levers with the 90 degree guide in the body cut that to 2500 miles. Weather made no difference - I only got wet about three times on my last rainy season cable, and don't remember any storms on the dry season cable.

There's always a noticeable sluggishness moving to smaller cogs and need for less tension to get acceptable shifting before cables break so I just pay attention and swap as needed.

Unlined right shift housings lasted ludicrously long for me; plastic lined ones seem good for about 5000 miles which is time for the next cable swap.

Brake and front shift housing makes it years before getting stiff and cracking at which point I also replace cables.