Indian culture or hinduism in general believes that God(s) are omnipresent, and touching something with our leg is seen as disrespecting the god inside that object. This is not only related to Hinduism nowadays, I've seen many other people following different religions do the same... ig its now become an Indian culture kinda thing

While growing up as well, if something had fallen on ground we were always encouraged to pick up the item by hand, and we were discouraged from picking it up using our legs, and now it's become a habit... you would rarely see an Indian pick up a fallen item using their leg

Books are given high respect in our culture, and Hinduism also has a god who is said to reside in books.. the god of knowledge, basically similar to athena in greek. Other religion people also hold the same amount of respect for books... hence why most Indians might feel bad while walking on that kinda floor