how come?

Something I've never understood is when people insist you take your shoes off to be a guest in their home, but when you put your shoes back on to leave your socks are dirtier then if you walked outside in a mud hole. I mean, I understand common courtesy completely. If my chosen foot apparel are caked with crud from mucking the stalls or if I just stepped in dog poop, then sure I'll take them off at the door. I totally get that. But come on! Whatever happened to making your guests feel comfortable no matter what they have on their feet. Maybe they don't want to mop your floors with their white socks that day. Maybe they would like to keep the forgotten bits of playdoh, five pounds of dust and dog hair on your floors instead of taking that home with them in their shoes.