Because the only real way we have to determine the quality of a developer's talent/expertise is to have someone equivalently talented/expert make a subjective e

Because the only real way we have to determine the quality of a developer's talent/expertise is to have someone equivalently talented/expert make a subjective estimate based on seeing lots of examples of their work. And even then it's a bit of a crap shoot. What employers are doing when they look at years of experience and so forth is trying to hijack the process of evaluation. If you see that someone has been working at some prestigious company in an important role for years or they've been promoted while working there, and so on, that gives you a little bit of insight into what that organization and that person's co-workers think of their skills. If someone has managed to stick it out in the industry for some number of years it's less likely that they are just faking it. The core problem here is that assessing a tech worker's skills and potential is something that could easily chew up millions of dollars in resources to get a good answer, and easily many tens of thousands of dollars to get a pretty crappy answer. Instead, employers choose to try to get answers to the question with one or two orders of magnitude less in resources expended. That's all it is.