IQ, flawed as it may be as a measure, is sometimes touted as one of the best predictors of success in life. It's just conjecture, but maybe there's a feedback loop there.
Zip code is also a very good predictor of success in life. IQ could be a great predictor, but that still doesn't mean it's measuring what we think it's measuring.
IQ works just as well within families as it does between them, meaning that it predicts difference in success even between children in the same family.
I'm not going to claim that IQ quantitatively describes some useful aspect of individuals. I'm not trying to justify a natural aristocracy. Moreso if we actually did identify this relationship between long term success and high IQ scores then maybe we can identify paths to success through other measures.
Again more conjecture, but maybe IQ has more to do with concentration and abstract thinking. If there were a relationship between wealth and childhood trauma/stress that could impair abstract thinking, it would make a good case for policies designed to prevent childhood trauma, in particular those brought on by poverty.
So you think it "very unlikely" that someone more intelligent would make better decisions, and those decisions have better outcomes enabling someone to live in a pricier neighborhood?
Well first, we're talking about the zip code one is raised in not the zip code one ends up in later in life. Second, we're discussing the efficacy of IQ as an actual measure of intelligence. You're assuming IQ is a good measure of intelligence in order to prove IQ is a good measure of intelligence. Sure, zip codes are a proxy for IQ if we accept that IQs test something other than just intelligence.
Finally, the causal relationship you have set up between intelligence and quality of living situation, while undoubtedly true to _some_ extent, ignores everything we know about system racism, system sexism, our horrific healthcare system and a host of other factors that complicate this idea - at least in the US.