It's the equality vs equity discussion based in geography
There are certain sorts of facilities which will almost never be available alongside small towns. It's not just "expensive" to maintain something like a Level 1 trauma center - if it were lightly utilized it would be economically unviable. It is something that will not exist away from a city.
That's an extreme example but even more mundane medical facilities end up being very expensive when you push out into rural areas. That those areas tend to be economically depressed, at least in the US, makes the problem that much more serious.
Why not? I think it's a natural conclusion of that fact.
Should every small town have a Tier 1 Hospital? A world-class university? A national sports team & stadium? An international airport? A symphony orchestra?
Don't get me wrong, I grew up in a rural area and have a fondness for it, but I do expect that rural areas and small towns should reasonably have less facilities than major cities.
This almost describes Alabama.
That's why the hometown tax exists. Small towns use their residence tax money to raise children then none goes back in when the young adult moves to Tokyo and pays residence tax there instead of in their hometown.
Singapore is just a city. Hong Kong for a long time too. The Netherlands is functionally a very large low-density city with some high-density parts. And in some countries, like Saudi Arabia and the UAE, the small towns are economically non-existent compared to the cities.
I don't know how a large country functions, but for the Netherlands there is a clear need to invest more in the rest of the country.
I just moved to the Netherlands (in the Randstad) and it's arguably better for the country that I moved to a place that already is dense and efficient to provide services to. Though it would be nice if it were above sea level.
One thing I will say though is that the area outside of it - pick any direction - is idyllic and doesn't seem to be struggling economically. Loads of local businesses, loads of people just going about their day, buying houses, having kids, etc. It's idyllic and I don't really understand why all the activity seems to be in the Randstad.
I mean I do get it, it's a chicken / egg problem; talent travels to the cities because that's where the best jobs are, the best jobs go to the cities because that's where talent is.
But I would like the government to incentivize more "work where you live" schemes; smaller sattelite offices for larger employers, remote work (obviously), extra income and subsidies if you work remotely (because of reduced office costs and to discourage commuting, since our roads and railways are all full up).
If anything it's a good thing - it means investment in Amsterdam benefits far more people than just those in Amsterdam.
Which of their neighbors do you think Japan is safe to rely on to feed their population?
edit: Note that China just the other day extended their 9-dash line to a 10-dash line
At the risk of stating the obvious, the point of my question wasn't to literally determine whether any big cities exist without heavy industry nearby, although that would be sort of interesting if it were the case. The point is that any such city is going to be an exception to the utterly ludicrous statement of the OP, "Because you really don't want heavily polluting industries (oil refineries, chemical plants, steel mills, etc) close to a big city." Big cities have always had this. The people there do not "want" them there any more or less than people in a small town would "want" them there.
Ir's not that different. If you concentrate economic wealth in cites, the periphery starts to suffer economically because it can't exploit local resources effectively, and the population starts selecting for city activity. Over generations, that leaves you vulnerable agriculturally and militarily. If you experience a natural or military disaster that deals a massive blow to one of you key cities, the whole country can collapse.
edit: Note that China just the other day extended their 9-dash line to a 10-dash line
In small cities you among other things have more agriculture and different forms of industry are also commonly pushed out of big cities.