As I recall, I remember buying cassette tapes- blank and pre-recorded- a bit earlier than 1972. In fact, I am sure I did- by '72 I'd been listening to cassettes for some number of years. For the time, they were not bad- track width was exactly the same as the more popular 8-Track tapes. I went with cassettes because I could make my own tapes (rare to find an 8-track recorder) and you could store almost 4 cassettes in the space ONE 8-Track ate up.
Given their humble beginnings, it is amazing that cassettes got hot-rodded to the point of rivaling open-reel, and have lasted as long as they have.