Not sure they were ever intended as Mountain bikes tbh.
That’s what they used to go wherever they could, it’s not like most roads back then were anything more than grass, mud or gravel tracks.
It was only 25-30 years ago mountain bikes were now what are essentially gravel bikes.
Classic steel frames, 1.8-2.1 tyres if lucky, rigid forks or maybe a smidgen of travel, narrow flat bars with huge bar ends. All pretty rough looking.
I had the below first time round (not my pics), I rode the same trails on those that I now ride on AM Full Suspension or Hardcore Hardtails, albeit faster and in more comfort now.
The raleigh activator was everywhere in the early-mid 90s. In terms of mass produced over saturated ugly bikes that prob wins by volume….