This is the crux of the issue. The Linux ecosystem philosophy is rooted in choice. Normal users don't want and/or need that much choice.
Average Joe doesn't care what an operating system stands for, or how involved the developer community is, or how customization a system is. They need a spreadsheet/internet browser/email machine that can run some misc. business software, but most importantly they need something that just works.
For all of the benefits of using Linux, the one thing it has never nailed down is intuitiveness. Say what you want about the (many) flaws of Windows, but you can't deny that one of the easiest out-of-the-box-this-thing-just-works experiences. It's also the same experience every single time you use a Windows machine.
Try explaining the difference between Arch, Ubunutu, and Debian to a normal consumer and their eyes glaze over before you even begin.