I solved it. For anybody else having the issue, here is what I did.
First to replicate the issue: I was installing IIS by choose “ASP.NET” in the Add/Remove Windows features menus. This was selecting everything needed for IIS to run .NET apps, but interestingly it couldn’t serve static pages (.html, css, js etc.) My test page was just a hello world .html page, so that is why it wasn’t being served.
To fix it: To enable serving of Static content you must specifically choose “Static Content” under Common HTTP Features in the same Add/Remove Windows Features list. Once you do this my test page worked fine.
In summary: I don’t understand how a typical .NET would run without static content (CSS, Images, Javascript), so I don’t know why MS wouldn’t include Static Content by default when choosing ASP.NET. Perhaps my workflow in installing IIS was wrong.
I’m sure there was a way to trace the flow of the request to find static content requests were getting blocked, but I don’t know how to do that.