Do you bleach them? My kids' white socks last longer when I don't, but I hate soaking them for 24 hrs in regular detergent to get them white so I usually just bleach and rebuy!
A really weird possibility that happened to us: The grout on our tile floor rubbed holes in our socks! I figured it out because I was the one in the kitchen on the tile the most often and my socks got holey the fastest!
Funny, my boys WHITE socks use to look horrible. We never bleached or soaked them. I never even thought or considered that once. Typically I just tossed them when they started to look too bad. They only like the no show socks anyways, so it doesn't matter how horrible they looked. DH started buying black socks now black socks are all he and the three boys wear. The black socks are great because they don't get that ugly/dirty white sock look. They are still no show style socks.