> How/why do you not promote the growth of denser, middle class inner city neighborhoods with a diverse profile? Is there a positive reason to not encourage it?

They do promote it. Every city in the US is promoting inner-city neighborhood development (commonly called "gentrification" here). It's just not usually a great for actual citizens.

Dense construction is always more expensive, so anytime density goes up, your immediately paying a lot more money for a lot less housing. And property in the US is valued exclusively by it's density (what realtors will call "location, location, location", but really just means "how much stuff is around it -- how dense is the area"). Living near density (even if your own property is not dense) always costs a lot more money, which means your again paying a lot more cash for a lot less housing. Alternative public transit options are poor in most places, but simultaneously, most inner-cities are actively hostile to our current universal public transit (cars), so the closer you live to the center of town, the harder it will be for you as a resident to get anywhere regularly, and you'll be transportation-disadvantaged compared to any of your friends in the suburbs. And because it's more expensive to live there, the taxes there are almost always much higher (since the tax you pay is based in large part on the value of your home, and houses near the city cost more, so you also get to pay more in taxes).

And, since families generally don't have lots of money to spend, they are in the same boat as you, and almost entirely pick suburbs (to save lots of cash and get better transport), so their kids all enroll in schools out there, so the quality of the schools out there is a lot higher, which makes future families more likely to make the same decision.

And if you have anything "tricky" happen to you (perhaps a elderly family member needs support, or you get divorced, or your kid becomes disabled, or similar), any and all of the assistance you might want or need to help deal with that, is also easier to get out in the suburbs. And since your cost of living is lower out there, if you need extra cash to handle a problem, it's easier to financially float that in the suburbs.

The model is crazy, but it's not crazy at the person-level. It's mostly crazy at the federal level. The government could let properties actually depreciate, so that renovating old properties inside the city is cheaper than building new out in the suburbs. But that would require them to let property values fall in urban areas so that housing can become affordable, and cities as well as all rich people are always 100% against that idea. So instead, federal policies prop up artificially high property values in urban areas, with the net effect being a semi-explicit policy that cities are not for most people. The goal is that anyone not single/20-something/wealthy, should not ever actually live there, and these policies are mostly successful at doing that.

> If local taxes were done at a uniform rate statewide, would it help

Probably not. The problem with local taxes is not usually that the rate is much higher, it's that the cost of living in a city is much higher, so your property itself costs way more, and that means you pay way more in taxes (even if the rate were hypothetically exactly identical in both, you'd still be paying way more in taxes city-vs-suburbs, because urban housing tends to cost way more to buy, and the taxes you pay are based on the sale price of the property itself)

> Building standards which means construction of "depreciation homes" is not viable

This is a good idea, but it would actually help the suburban sprawl far more than it would help the city (since lower density is more affordable), it would encourage people to stay in suburban sprawl longer, since those properties would still always be cheaper, but now (under this new rule) would also would be better built and last longer.