While the forms work perfectly in Adobe Reader or Internet Explorer, Chromium-based PDF viewers don't have the ability to use certain Adobe PDF API functions, like submitFormAs or mailForm. Even more problematically, the old Edge doesn't even have this functionality. Now granted, its not a major issue for Windows users, but the fact that you either have to use a decades-old web browser or download a separate 180 MB program just to access a simple PDF form is a real annoyance for a lot of clients. On top of that, Safari doesn't have API capabilities either, so you're pretty much screwed if you're a Mac user.
I believe that it would be a massive boon if Microsoft brought back the same functionality for PDFs that they had back in IE. It would give me a bunch of people to switch over from Edge to Chrome. On top of that, it would increase cross-platform interest for Edge for Mac and Linux, as well as anyone who doesn't want to deal with Adobe's BS on a day-to-day basis.