I think that reason is mostly inertia. Also, because it's GNU. Just as IE is the Microsoft browser, bash is the GNU shell, and most Linux distributions are bui

I think that reason is mostly inertia. Also, because it's GNU. Just as IE is the Microsoft browser, bash is the GNU shell, and most Linux distributions are built around GNU userland. But that's just Linux. The BSDs don't see bash as the best default, where it tends to only be available as an optional package.