This matches my experience as well (I suspect it might not in less urban areas, though). It's quite frustrating.
I also resent the fact that the people who are accosting me like this usually have the expectation that I owe them my attention. I'm pretty good at brushing them off/ignoring them, and I've seen quite a few get genuinely offended that I'm evading their pitch. Which is offensive to me in turn: they're trying to take advantage of my natural inclination to be social/respond to another human, and they're mad because I didn't fall for it? It's a parasitic situation. Sadly, I also agree with you that there's not really any way to fix it. The well is just poisoned...
