Terrapin_Station

Which is part of why you don't know what you're talking about. You're ridiculously, simplistically thinking that it necessarily has something to do with Billboard charts, and you're not even bothering to think about just what it was that Billboard charts were keeping track of in the 70s/how they were keeping track of it (not to mention probably not being aware of the fact that Billboard chart positions could be bought back then).

Also, if you're in the UK, I can't say much about what was popular or not, or how relatively popular anything was, in the UK in the 1970s. My knowledge is of the US. There are a lot of things about UK culture that I still don't understand very well, including that to my knowledge, how radio stations are run is--or at least was--completely different in the UK than in the US. Radio culture has also changed significantly many times in the US over the years, which is one reason that Billboard charts are much more significant now in telling you what's popular on the radio than they were in the late 1960s through the early 80s. Another reason for that is that Billboard has changed just what it is they're tracking and how they track it over the years.