It's important to mention that the counterculture "punk" part was simply an totally extraneous embellishment to make the story "cool." The noir part is a perennial pulp crutch to make things seem dark; it's simply a coloring of addiction and betrayal.
Gibson is doing something with that: he's saying that technical culture has ceased to be exclusive and elevated, and has become part of the fabric of human existence. Just like his broken prism-Hemingway prose says something about the nature of identity when there so much of it is virtual and artificial.
But if there hadn't been a "punk rock" substrate in the mid-70s to mid-80s to associate with people who weren't wealthy - if there hadn't ever been garage rock - then he'd probably have had to express the same thing through Steinbeck-style techno-field workers and Upton Sinclair derived techno-socialist plotters. He's inspired by computer criminals, which are really an unimaginable thing right before then - the closest analog might have been counterfeiters. A subculture immersed in high technology. Maybe clandestine LSD chemists are somewhere in there.
He still, as most all vulgar "cyberpunk" derived stuff still lazily does, would have been able to rely on noir tropes. And note how the "Yakuza" is simply a stand in for 1920s Chicago gangster tropes, but given a global edge because of his vision that the virtual future would collapse distances.
The "coolness" was utterly shallow, and instantly became assholes stapling circuit boards to leather jackets. Or "steampunk," which was exclusively a surface aesthetic for people who thought that technology was too hard to reason about, so they just decided that if tech was simply magic, why not just do fantasy at the dawn of the industrial age? Dispose of all of those pesky questions about identity(s) and just ask "wouldn't it be cool if..."
edit: there were people working in the same vein at the time, the Semiotext(e) SF anthology and the Mirrorshades anthology showed what cyberpunk (and cyberpunk-adjacent) thought of itself; questions about identity, reality, and linearity; and their interactions with communication and simulation technology. They were ignored for noir retreads with circuitboards and leather jackets. Almost immediately it was saturated with childish fantasy - actual hackers working on Tolkienesque "cyberpunk" roleplaying scenarios for Steve Jackson Games. Ironically the situation ("E911") around creation of a childish, escapist "cyberpunk" product was a historical expression of the actual themes that the cyberpunks were largely chasing. No wonder Sterling (also fairly pulpy writer) wrote the definitive account.