"Almost any Python command line program" seems to be an exaggeration. It relies on the command-line program using argparse, and explicitly doesn't work for any that rely on optparse, which, sure, is older, but also means that things which rely on the popular Click command-line library won't work either.
Which is arguably a good reason Click should look for an alternative basis (though, OTOH, the reasons Click remains on optparse are, arguably, a reason that optparse, while it perhaps should not be further developed but for bug fixes, should not be considered deprecated), but in fact a lot of Python command-line programs depend on Click, so something that only works on argparse-based programs does not, in fact, support "almost any Python command line program".
