I don’t think mountain biking of that type would ever have been pioneered in the UK, as we don’t have big enough hills.
Mount Tamalpais is 786m according to Wiki. That’s bigger than the hill I can see from my window, but I can get to a 500m ascent/descent fairly quickly around here – do I need the extra 200m to make it proper MTBing?
Blasting down fire tracks at speed uses up the average UK hill pretty quickly.
What do you think we used to do in the early days in the UK, ride around canals? ‘Oh don’t bother going up the hill, we’ll be back down too quickly..’