Unsupported by the usual suspects, that's why.
edit: and I guess a JS shim can be used if it really matters.
In no small part due to Microsoft's decision to make IE11's rendering engine the only browser that could support: Java Applets, Flash, ActiveX, that almost all major companies and large governments use. If they had incorporated those into Edge and hidden them behind ten layers of security warnings, we wouldn't be in this mess.
Try to service large corporations and governments. Our IE11 user share is over 70% for the product (but under 30% for the marketing/public pages). This won't change until every last Java Applet/Flash/ActiveX control dies, and that isn't happening fast -- companies literally in 2019 still sell products using the tech' (Oracle!).
I was excluding this from the "most cases", but thanks for the wake up call anyway. Outch.
Yes this is too bad. Great feature.