But the thing is that the iPod wasn't the first to market for that either.
I remember having the https://en.wikipedia.org/wiki/Personal_Jukebox and loving it before the iPod came along.
I don't think it was just the storage size that was the difference. It was the combination of a well designed simple UI together with excellent marketing that seemed to make the difference.
400mb/s Firewire let you actually put a lot of files on it in a reasonable amount of time. The theoretical 11mb/s of USB 1.1 was painfully slow in comparison.
The ipod was _tiny_ compared to the other hard drive based mp3 players of the time.
Also, on the iPod you could browse your music in an organized fashion (e.g. by artist), whereas with other mp3 players it was just a long list of tracks.
There's always been better mp3 players but normies don't know about them.
Most MP3 players at the time had around an hour's worth of storage. The Creative NOMAD was 64 MB. That means those products were from a user experience perspective in the same category as Walkmen and Minidisc players. It was a writable music player that held about an album. It let you make your own mixtapes, but selecting media while at home was a fundamental part of the user experience.
The first iPod had 5-10 gigs of storage. You didn't have to decide what to listen to before you left the house. You just put everything on there and decided on the fly. This was a completely different experience.
Whether the little box played MP3s is essentially an implementation detail. It was the storage size that made the iPod an entirely different "it" from the devices that came before it, because the way you used it was so different.