Why is only the top half of a body viewed during a funeral?

This custom is by no means universal. I have seen a number of Italian-American ladies laid out- full length- and the effect was stunning. Possibly the half-couch or ( playing card) presentation may be inspired from... indeed, playing cards. May be done to show a sleep-like posture. There is nothing wrong with full length and if it is a beautiful woman, well it only enhances the illusion of being Natural. of course if there is surgery or battle damage ( for example auto accidents which might damage the legs) one can see the half-length presentation. Both have their uses and devotees. The body is normally barefoot in the half-length presentation- so the song ( Christmas Shoes) sort of shorts out.