I have asked the developers the same question. As you know, you can use any browser to see a browser preview, but the 'external' preview is different. It has been IE all the time I've been using the Editor, only changing to newer versions as they appeared. The app and the IE 'engine' seem to be quite involved with each other, and as far as I've heard, it actually takes quite some brain cells to dissolve that relationship. That's all I know about it.

Yes it was that way since I got the Editor back in the dark ages.

New Chrome Edge Location
c:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe