Last time I looked through the YC alumni list (http://yclist.com/) I was surprised at how heavily it was skewed B2C though. I haven't checked since W15 was added but a quick skim and it still seems fairly B2C focused.
It's in their request for startups though. Seed funds don't seem to be an area that attracts B2B.
I suspect it's because you have to be in the industry to understand the problem exists in the first place, so a huge segment of the YC applicants simply don't know about those opportunities as they've not worked in industry and only know about B2C opportunities.
YC is not the VC industry as a whole. For one thing, it (like SV) skews much younger and much more consumer than VCs in general. There are plenty of VCs who invest mostly in B2B companies started by founders with domain expertise.
It's in their request for startups though. Seed funds don't seem to be an area that attracts B2B.
I suspect it's because you have to be in the industry to understand the problem exists in the first place, so a huge segment of the YC applicants simply don't know about those opportunities as they've not worked in industry and only know about B2C opportunities.