Genuine question for the shoes-on people: why don't you bring your own slippers or pair of clean ballet flats?
Because it just wouldn't occur to people who aren't totally preoccupied with shoes off. Non-anal types don't even have it in their head to think about it, let alone to plan ahead and pack a pair of slippers / flats in their handbag (which probably isn't even big enough to hold them), let alone expect to faff around with needless shoe changing. It's a totally different mindset, compared the mindset obsessed with shoes off.
My default is to assume people are welcoming hosts and besides, I'd just offer to take my shoes off - sitting around in someone else's house in my slippers would just feel completely inappropriate (like going out in pyjamas).
As for slipper/sock baskets, the only place I've ever encountered them is on these threads. No-one IRL does this.
This ^ by dowgercuntess.
Who the hell would carry their own slippers to wear in someone else's house? That is weird. And ASKING someone to wear slippers they provide for you. That is a whole new level of weird!
Out of all the places I have ever visited, all the countries and towns, all the people I have known, and all the friends I have had; I have never had anyone ask me to take off my shoes and wear the slippers that they provide.
Unsurprisingly the people asked by several posters to post pictures of their slipper and sock basket for visitors, have not posted any pic. SURPRISE SURPRISE!!! PMSL!!!!!!!!!!! 
Probably because as you said cuntess, no-one in real life does this. It's a load of shite, like much other stuff that certain people have spouted on this thread.
As I said earlier in the thread, the only people who have asked me to remove my shoes before entering their shitbox of a house, are obnoxious dicks who think they're something they're not, and who think they're middle class.
And as passport said, how the fuck are people going to cope when their child starts crawling around/running around/playing around outside if they are so precious about dirt?! 