At the time though it really felt everyone would one day own an mp3. The entire world had a walkman. The mp3 player was like a 10x better version of that.
The Walkman was a hugely successful product, but I don't think that everyone owned one. It was popular with teenagers, exercise/fitness enthusiasts, and a few other categories. It wasn't something that a businessman would have owned, or an elderly person, or a poor person. Today, however, all of those people own smartphones.
I really think it was the iPhone that changed Apple.
Everyone had a little radio/tapedeck/cd player. I had like a half dozen of these devices laying around my home. You go on a walk and everyone has one of these things strapped to their hip. I assume business people still want to listen to the baseball game taking the commuter rail home.
Wikipedia cites an article in Japanese saying that about 220 million Sony Walkman devices were produced before discontinuation in 2010. Even if you quadruple that for other brands, you're not even close to 1/4 of the world at the time they first came out.
I don’t think you will ever get full numbers. People in Kazakstan or kenya in the 1980s definitely had this sort of thing but I doubt it would be a first party sony walkman product. A portable tape deck/radio is cheaper than a larger stereo.
