But it absolutely is. It is not about 16, 17, or 18, it is about getting the best possible score. That's what you're saying. If it is possible to take a better score, people do so. So literally only logical solution to this is that everyone just has the same number, no difference can exist.
I've actually been thinking about this a lot over dinner. I agree with the first part, but not your conclusion. It
is all about getting the best possible score, but I think that's only because the game doesn't offer anything else sufficiently compelling to trade it for. I mean, at higher levels people are
sometimes willing to trade the higher score for a feat, but we don't know what people are willing to do at 1st level because the only way to get a feat (vHuman) also lets you get a 16.
Which made me think of a possible compromise solution. (I mean, not that any of us have any influence over D&D's design, but let's pretend it's like fantasy football, but....fantasy game designer.)
What if races got a +1 ASI, sub-races got an additional +1, and then there's an additional floating +1 that can go anywhere, including overlapping one of the first two. So fans of racial ASIs for historical/traditional/thematic reasons would still have that, and the only races that could start with a 17 would be those traditional archetypes, but
anybody, with any race/class combination, could start with a 16 in their primary stat.
I would still prefer just a floating +2/+1 for simplicity, but I would also be ok with this +1/+1/+1 solution.
Why?

I mean, sure, people are free to make such a choice, but to me it seems utterly absurd though. This is a roleplaying game not a competitive wargame.
It's not a competitive wargame, but that doesn't mean people don't get satisfaction from mechanical effectiveness. And although the "why" might be an interesting question to explore, the reality is that it's what a lot of people do (based on D&DBeyond data.)
I mean, I am equally boggled by some of the practices espoused in the name of roleplaying. But, hey, it's what some people do. And I know that trying to rank playstyles in order of validity, and to claim that one is better than another, is not really a useful or productive way to resolve the kinds of questions we're talking about in this thread.