The confusion is that the "Bash.exe" that you run to initiate the WSL subsystem is entirely unrelated to the bash, the shell that gets executed in that subsyste

The confusion is that the "Bash.exe" that you run to initiate the WSL subsystem is entirely unrelated to the bash, the shell that gets executed in that subsystem. In the cygwin scenario, when you ran bash.exe - you really are running the bash shell.