Self interest

Excellent idea. However, if the distro vendors did this, they'd probably 
do it for their stable enterprise kernels, as those are the kernels their 
paying customers use (and also kernels that change slowly enough that this 
sort of fine tooth-combing is possible).

I wish this sort of thing was possible to fund with the raging high-speed 
chaos that is upstream kernels but I have a feeling that it isn't :/ 
still, hopefully if this were done *some* of the holes that were found in 
distro kernels might still be applicable upstream.

(disclaimer: I have no input into funding decisions anywhere at all nor 
ever have had. This is purest speculation.)