What was the significance of foot washing and why is it not practiced today?
Footwashing started out as a cultural thing. In ancient times people wore sandals and walked on dirt roads. As you can image this meant travelers would end up with dirty feet. Therefore as a gesture of hospitality hosts would offer their guest a chance to get clean. Depending on the circumstances this could be done simply buy providing water for the guest to use. Some times a servant of the house would wash the feet.
Now in our days dirty feet is not such a common problem for travelers, so washing of the feet is not part of our cultural and hospitality ideas or understandings.
From a religious aspect it gained significance when Christ washed the feet of his apostles. Part of the reason why Christ did this was to show, by example, how the greatest in the Kingdom of God is the one that serves.