I too was wondering why you can't just start microsoftedge.exe, like you do "old-style" applications in windows 10. Searching the web, I found the answer -- it has to do with how Microsoft implemented "Universal Apps".
Below is a brief summary taken from that answer, but I recommend reading the entire entry, because it gives a great explanation of how these "Universal Apps" are being dealt with. Microsoft Edge is not the only app like this we'll be dealing with.
Here's the link: http://www.itworld.com/article/2943955/windows/how-to-script-microsofts-edge-browser.html
Here's the summary from that page:
"Microsoft Edge is a "Modern" Universal app. This means it can't be opened from the command line in the traditional Windows manner: Executable name followed by command switches/parameter values. But where there's a will, there's a way. In this case, the "way" is known as protocol activation."
Kudos to the author of the article, Stephen Glasskeys.