Writing a script has always been simpler than making a proper installer, because you need to adhere to various transactional rules, implement a proper rollback mechanism, worry about making your components have correct keys that still work after an upgrade. And e.g. if you need to install a Windows service, most of the standard options (even those provided by Wix) don't cover all cases out of the box. So to some extent using a script means replacing a more complex, but complete solution with an ad-hoc thing that may work in general, but fails a lot of corner cases.