Why does Microsoft Edge (formerly Project Spartan) prompt to open this website in Internet Explorer?

Question

Does anyone know what triggers MS Edge to not open a specific web page/site, but instead prompt the user to open the site in internet explorer?

The message says:

Answer 1

You must send an email message to Microsoft(iepo@microsoft.com) and request Microsoft remove your site domain from the Compatibility View List.

https://msdn.microsoft.com/en-us/library/dd567845(v=vs.85).aspx#removal

To remove your site from the Compatibility View List (or to dispute the removal of your site from the list), have the overall site owner verify that the domain site appears in the Compatibility View List. If it does, send an e-mail to iepo@microsoft.com that contains the following information:

• Owner name
• Corporate title
• Company name
• Street address
• Email address
• Telephone number
• Website address

Microsoft will review the provided information and remove your site from the Compatibility View List at the next scheduled update.