The destruction of gear sets is something I have never fully understood.

I've had the same gear set in my Mini since I got it in 2010-ish. There are no secrets or tricks whatsoever in the way I build it - I just follow the manual. Lubrication is next to nothing, just a little silicone oil.

Yet some people I race with seem to go through them every few race meetings.

Apart from the obvious stuff like crashing a lot and/or running a very tight diff, I don't have any real answer. It just isn't something that has affected me.