Wel Robert, if it is a compelling reason I don't know, more of a personal oberservation, these points come to mind:
1: I've indeed always thought one could with a long lens shoot streetstyle portraits of people while they are not aware being photographed (or even more important: not slap you in the face because they don't appreciate being photographed at all..) thus creating a different sort of portrait, which I thought at the time was nice. However looking back and re-evaluating these about a year onward they seem less special, or as a good friend and honest reviewer put it: they "lack" something...that "something' might be intimacy or a true personal connection between photographer and subject...i really don't know. Not that they are really bad pictures I think, otherwise I'd had deleted them, but maybe they show what I mean:
Here's three examples of these, taken with a 300mm on APS-c (450mm FF equivalent).
https://www.flickr.com/photos/kickmansch/14847688176/in/dateposted-public/https://www.flickr.com/photos/kickmansch/15240269212/in/dateposted-public/https://www.flickr.com/photos/kickmansch/15261812075/in/dateposted-public/2: Isn't Streetphotography (as clearly opposed to Landscape) mostly about "growing a pair of brass b@lls", getting out there on the street, putting your self on the spot, when necessary communicate with total strangers, wait endlessly, beg, or be bold etc, etc.
and then come away with that great shot, maybe a few. In many of this sort of photographs I like how the field of view of a wide-ish angle makes it look like the viewer is really inside the scene photographed, impossible with a (very) long lens.
Best Regards, Sander