The answer is simple: for the same reason that we care about and discuss how religious values compel us to advocate for the least powerful. For the same reason we debate and argue over the role that our experiences as people of color play into our consciousness. Or our class experiences and how they form our opinions of what transpires around us. Those values, experiences and backgrounds are like the air they breathe. You can try and leave them, but they'll never leave you. For me, the values I learned in the punk scene and from punk music continue to resonate, long after I stopped being a participant in any formal scene, and long after I stopped being up to date on the latest releases and what moves the kids these days. As Frank Turner sings--"All the latest music fads all pass me by and leave me cold, and all the kids are talking slang I won't pretend to understand."
If you want to start a discussion about the connection between the spirit of punk and the labor movement I find myself a part of, you have to start with what 'punk' means. Which is nearly a useless endeavor. How can a scene that generated GG Allin and The Appleseed Cast have any common thread? At the risk of being called a coward for not even trying to answer that question, let me say this: lots of people have tried to nail this down, and it's very tricky business. I think that the most you can really say about what 'punk' means is to narrow it down to what it means to you.
So, having listened to this music for the entirety of my adulthood, here's what it means to me: it's the total democratization of music, its production and its distribution (a very labor-oriented project). It reprsents a fight when the odds are so ridiculously stacked you have no hope in hell of winning. It's a jubilation more buoyant than any sugar high you've ever felt, and it's a total anger over things that you never had any control over. It's valuing humans and humanity. It's the beauty of profanity, sex, drugs, and rock and roll. It's a sick joke. It's the total rejection of the privilege life handed you so that everyone gets a better deal, or as Propagandhi puts it so nicely:
"And yes, I recognize the irony that the very system I oppose affords me the luxury of biting the hand that feeds. But that’s exactly why privileged fucks like me should feel obliged to whine and kick and scream- until everyone has everything they need."