Because on the shell side you want simplicity and on the programming side you want control. Shell pretty much has to default to "foo" meaning "execute command foo from $PATH" or almost every line will have useless overhead. GP language needs to make that explicit or it will be a footgun where you don't know what's a command / variable / function. And that's before we get into how the file descriptors / redirects are handled.

One shell which tries to merge those is ipython with the sh profile https://ipython.readthedocs.io/en/stable/interactive/shell.h...