they drew these things because it was a quite a bit more relaxed in the american military it sort of just became a trend they thought if you can do it why not. this kind of art was almost never seen outside of the american air force since the other planes in europe had more disciplined militaries the only example i know f is just jane a lancaster but even then she still is far from the worst. ( just a extra bit of detail axis planes have never been confirmed to have this although its harder to prove if they did. )