Prohibition of Leather Shoes During Shiva

I recently sat shiva for my father, may he rest in peace, and was reading the laws of mourning. One thing that struck me was the instruction to refrain from wearing leather shoes. It offered no explanation, so I did it just because it says so, but it’s been bothering me ever since. What do leather shoes have to do with mourning? Why are other leather garments such as belts and jackets permitted?