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

It is because the website is using some legacy technology. Microsoft Edge will automatically determine this and prompt the user. You'll need to figure what legacy components are there in Internet Explorer and convert those pieces to modern web standards.