To stock waterproof overshoes in a full range of sizes (particularly anything not XXS or XXL) - according to the first 5 bicycle shops in Edinburgh that I sampled today.
I ended up having to point out at the 4th shop that the "season" for waterproof overshoes in Scotland generally runs from 1st January through to 31st December.
Hurrah for the Bicycle Repair Man who stocks a full range of sizes and flavours