Lots of very successful software was built using a waterfall approach. It's a methodology that works well if you know precisely what the end result needs to be. That doesn't make it appropriate for everything - if you don't know what the customer needs, or if you want to get an MVP out, then Agile works better, but you shouldn't dismiss an approach because it doesn't work everywhere.

Plus, 'agile' in quite a lot companies is really waterfall that's been broken into sprints without the planning of proper waterfall or the discovery and learning of real Agile. The software still gets built though. Maybe software is actually quite easy to plan.

As if anything in the world is ever pure. Waterfall can have small scrums run on side-shows, while staying waterfally on the center project.

Because agile has been so successful, right? ;)