Because being a musician isn't to be solely measured by a metric of instrumental competency. The only thing that makes a person a musician is if they partake in the act of making music. Even if that music is just "throwing power chords together", as you so glibly put it.
The people that comprised the early punk bands may not have cared much for raw ability in playing their instruments, but to suggest that because of that they didn't care about the quality of their art is narrow-minded. They simply had different aims that they were trying to achieve. Where the more technical-minded musician is engaging in a quest to improve their base skill as a musician, the punk is playing music as a way to describe and promote an ideology, to give voice to frustrations, or for simple visceral catharsis. In these aims, instrumental skill is not a factor. But do you honestly think that there is no skill involved in constructing an effective punk rock song?
The issue here is that you assume a technically conscious musician doesn't aim to express themselves. Political, social and philosophical commentary isn't exactly unique to punk rock.
Perhaps my use of the term "pissing contest" was inflammatory, but do you really think that there is no small amount of competition between musicians of a certain type to see who can play faster and wilder than their predecessors?
I think that there is absolutely no competition whatsoever. I can't imagine how there could be. There are reasons to want to be faster, but I don't think ego is one of them. To produce more intense music, or to be able to play with more general comfort would be the real reasons to increase speed.
Stripping this pursuit of any value judgements as to it's worth, can you honestly tell me that it isn't a concern of some virtuoso musicians? If it wasn't, then how could virtuosic/progressive rock music even be a sustainable genre? The term "progressive" is a giveaway, which implies that when done right, the musician will be doing something which is considered new and different from what came before. From having moved among communities of progressive rock fans for far longer than I've been on this forum, I can say with all certainty that this is usually defined as involving some step-up in instrumental skill or in musical complexity.
My interpretation of "progressive" references song structure more than anything. I could explain my point of view for ages with numerous examples, but in short, the term "progressive" has far too many contextual hooks and traps in reference to technical skill and complexity, not to mention the way standards change over time. Taking "progressive" in the context of song structure, however, allows for definitive comparison. If we're basing this off technical skill and musical complexity, you may as well go ahead and say Led Zeppelin were progressive (although, to be fair, they were in the strictest sense of the term "progressive"), or that Deep Purple were progressive.
I think you're missing a vital point about punk rock that is a natural result of not being around when it happened the first time, and not being a fan of the music.
Punk music WAS groundbreaking and WAS experimental in 1977. Nothing like it had ever really been heard before by a great deal of the music-listening populace. It's also worth noting that by the time 1977 had rolled around, the genre of progressive rock had become incredible stagnant and formulaic.
I suppose I did claim it wasn't experimental through implication, but that wasn't really my point.
Also -and correct me if I am mistaken here- you seem to be discounting the role that lyrics and presentation (not the clothes the band wear, but the manner in which the notes are played, guitar tone, production etc.) play in the formation of a cohesive notion of music and you are judging a band's capacity to innovate purely on the compositional aspects of a song.
The voice is an instrument, and the melodies it expresses are a part of the compositional aspects. Expressing language doesn't separate it from other instruments. All the same rules and limitations apply.
I'd like to note here that I don't have significant emotional investment in this discussion. If I sound like I'm getting riled up, please understand that I'm not, and I want to continue this in the most sincere and comfortable way possible. I'm mostly playing the Devil's advocate here, as I understand the purpose of punk rock and its place, but I've never discussed it from the point of view of it being potentially regressive rather than progressive.