In my opinion, yes, WordPress is great for simple single page websites. Whether those single page sites are flat or not has almost nothing to do with anything, it’s just all semantics. One page themes can do wonders for presenting your content in a really appealing, eye catching way. Sometimes, all you need is a single page to create the right atmosphere for your readers and getting all the information out there in one page is a great way to do it. A lot of people enjoy simple and flat themes that are never boring, because a flat theme makes the reader take more not of the content of your site, rather than all the design elements your page might otherwise have. Flat themes, and their cousin the material design theme, are popular right now, it seems like I find a new flat designed website every day. I’m not sure how long this trend will last, but it’s been going strong for quite some time now, so I see no reason it should stop anytime soon.