Wouldn't surprise me if the company just heard that "everyone else uses Dreamweaver" and went from there.
WYSIWYG inspires lazy coding. It doesn't always parse right and though it gives you a preview, usually that preview is just how it looks in IE or whatever your default browser is. If you don't know what the underlying code of your website is doing exactly, then if you ever run into compatibility issues in other browsers or validation issues, you'll have no idea how to fix it. It's just smarter to use a text editor for web design. You yourself probably haven't run into this issues (nor will you run into them at all if you use such simple designs on your pages) but when you start getting into big, complex designs for large websites with pages and pages of content that need to be organized... you'll want to make sure you know the ins and outs of your designs right down to the code. :/
But so long as you aren't actually intending to go into web design and the like, a WYSIWYG editor should work just fine. They do exist for a reason and it's so that any layman can create a website that, for the most part, works and looks just like they want. But anything more advanced than a simple personal site and it's really worth your while to invest the time and effort into learning HTML and similar web languages.
