The upcoming reboot of the Edge browser (based on Chromium) will contain have a IE mode built in for accessing old sites like that. (Yeah, I know, what could go wrong?)
The reason IE is still needed by enterprise is that there are a ton of business applications still out there in the wild that depend on ActiveX components to interface with Office and other old Microsoft technologies. Replacing them would require a huge investment in many cases. Sort of like the vast amounts of COBAL code still in use in the business world, even though so few people still know how to code it.
Granted. Still, one should bite the bullet and move away from IE. Those Active-X applications are insecure, and risk losing the business. The only excuse for not updating and rewriting applications to get rid of old, buggy, insecure dependencies, is if the owners of the business don't plan to continue -- sell, bail out, etc.
Depending on Microsoft to keep supporting IE (or an IE-compatible mode) forever is risky, and leaving your network open to attack on the old known vectors of Active-X is even riskier.