Are the really old classics loosing value ?

I was watching a Youtube video where guys were walking through an auction warehouse checking out the bikes debating what they would sell for. The bikes with the highest reserve price was a Barry Sheene 750 and a Honda NS500 anyone at some point they looked at the 20's / 30's / 40's type DJ Run type bikes and the one guy talking about some classics loosing value said "but who will buy them ?" and the other replied "you are right the target market is all dead !". Now I know it sounds a bit crass but maybe true, we usually value something that was popular or we wanted in our youth and all those riders are as they said most likely passed on by now or late 70 / 80's. There are still plenty of boomers and gen X around that loves the 70's 80's bikes but they too will start getting less and less. Do you agree that at some point a bike becomes worth very little or drops quite badly in value ? Something like a Vincent Black Shadow maybe never but for normal BSA's and Triumph's maybe ? From 9:40 for reference