I am trying to figure out why people feel the need to put their feet on the bulkhead?

I was looking around while being seated in 1D (short haul) a few days ago and noticed that there were footprints on the bulkhead all over the place (unsightly!), and the man sitting in 1F had his feet on the bulkhead too. It did not even look comfortable because his feet kept sliding from the wall as he struggled somewhat to reach the bulkhead.

Why do people put their feet on it? Is it really so much more comfortable?

Also, haven't their mothers told them that it's ill-mannered to stick their feet on the wall or on an object other than a footrest?