Hedi's dedication to high product quality is probably a consequence of self awareness. Throughout his whole career he has always flirted with bad taste (Punk, Grunge, New Wave, Dandies, E-Boys) in his collections. When a designer is trying to sell an atypical aesthetic at a luxury price point, the quality level has to become a strong support to justify the price. Lots of 90s minimalist designers used a similar strategy.
You mean subcultures, not 'bad taste'. Bad taste is something like Gianni Versace, Cavalli, Dsquared, it exists often
unknowingly (meaning it came from lacking refinement, cultural capital, etc) in relation to what taste (aka. "good taste") negates (loosely quoting Bourdieu here). Subcultures, especially the ones you listed, tend to be nonconformist, critical, subversive at least in relation to their surroundings, and while they're not above strict sartorial dress codes
at all, and they do have a pyramid of status always, they don't exist in relation to the value of taste, and the way they enclose themselves means they're not actively pursuing it. Miuccia Prada for better or for worse, used to flirt with bad taste, that's what made her work 'clever' (lately she IS bad taste).
Hedi, just like Raf, Rick Owens, Marc Jacobs, what they all have in common is that they have built their fame on borrowing and/or shamelessly appropriating entire subcultures, watering them down, repackaging them, and reselling them to the rich man and ultimately the mainstream. They admire the subculture enough to turn it into their default gold mine and build their legacy exploiting it as a source and calling it their own, but not enough to seek credentials there and give up the wallets of the 1%. In the case of Rick, it's for the rich man who somehow thinks he's esoteric and 'weird'. In the case of Marc and Hedi, it's for rich people that for whatever reason never felt cool enough to go to concerts or be around certain people, so these two took the role of news correspondents and provide reports of what the cool and young people do and the places they go, and often times (because they know the airheads of fashion are not exactly fact-checking anything) they'll just make up places and moments and people and tell you 'this is it' and the fashion crowd thanks with a standing ovation lol. And because that need to feel and possess 'cool' runs that deep, it's not that the quality compensates for challenging or oh-so atypical and conceptual design, or that it finalises some process to convince consumers, that was never an issue for this demographic. The high standard of quality simply means they are from a relative old guard, a generation that came to the scene when the bar was really high and fashion is primarily their world (not the subculture they want you to believe). Delivering something 'cool' in s*itty quality back in 2001 just wasn't an option (unless you wanted to be talked about next to Imitation of Christ and not Jil Sander). They're well-educated and wired to a time in the industry where 'street' and superior quality were not antonyms.