Looking at https://unix.stackexchange.com/questions/380012/why-does-bash-interactive-shell-by-default-write-its-prompt-and-echoes-its-inter, in particular the first answer which has a link to http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/main%E2%80%8C%E2%80%8B.c  Made me wonder: why?