Surprisingly, casual Windows users have been "trained" to use Chrome and Firefox instead of IE/Edge, and Edge has the same logo so they know not to use it. So there's not much casual usage of Edge to begin with even though it's the default OS browser out of the box.

If Edge were multi-platform, then I'd consider it worth my time. But as Mac, Chrome OS, and Linux users continue to grow, I'm not going to waste my time making sure it works for a small amount of Windows users who barely even use the browser to begin with. Not to mention I'd need to dual-boot or run a VM just to test my work.