Because there's nothing even remotely standardized about high school education. A kid growing up in Seattle learns about evolution, while a kid growing up in small-town Oklahoma learns that Jesus rode a dinosaur to work. Cultural differences aside, a student who graduated #1 in a class of 50 probably enjoyed a fraction of the learning opportunities available to a child who graduated #12 of 500 at a larger school.
These are the problems that standardized tests were supposed to solve. Eliminate the tests, fine, but you'd better have an adequate replacement for them in mind.
I'm not arguing for their elimination. I'm sharing anecdotal evidence that they weren't useful for me and probably people like me who got an adequate education and had access to a local community college and a library.
Re: uneven distribution of education. This is the fundamental problem and standardized tests don't actually address the root cause. We really shouldn't be confused about what skills and concepts people need to learn up until high school and the rigor with which they need to learn them. Addressing this confusion is a hard problem so post high school standardized tests end up being the band aid. We can keep the tests and work to address the underlying root causes for uneven educational outcomes. Test preparation industry is essentially a form of tax on something that we should have democratized by now.
These are the problems that standardized tests were supposed to solve. Eliminate the tests, fine, but you'd better have an adequate replacement for them in mind.