Trainer blight

I know I went on before about the trench foot ballet slipper trend in London, but now that spring is almost here I have to ask:
Why do people wear trainers without socks?
a. your feet sweat,
b. your feet smell and
c. your shoes smell
not in any specific order.
Running shoes, trainers, sneakers, whatever you want to call them it's all the same.
Nuf said.