Because instead of infill density in cities, the sprawl will keep up its creep. Low density building makes that certain.
With how it goes with new development in American suburbs, it’s going to be car oriented and increase loud traffic and make walking unpleasant. (Although it’s probably already not very walkable)
Someone on the new edge will repeat your gripe, rinse and repeat.
As a bonus having more neighbors means things like grocery stores within walking distance become good businesses, so you need a car dramatically less and less space needs to be taken up by parking lots.
I assure you that neither of those are a good outcome as far as I'm concerned.
There's no way you're going to make public transit work in the American suburbs: you're better off hiring taxis and letting people use those for free, because at least the taxis won't create so much pollution and use so much fuel. Running buses every 10 minutes in the subways with 0-2 riders will never be practical.
Maybe western countries should learn a lesson from this, instead of somehow expecting public transit to always operate at a loss. The transit itself makes land valuable, so why not use that as an opportunity for profit? Here, even inside the stations, they rent out space to convenience stores, vending machines, cafes, etc., so they make direct profit just from that, but over in the US they seem to be allergic to doing that (nor do they even have bathrooms in the stations!).
Aside from lawn equipment, the noise pollution I suffer from in my streetcar suburb in a major metro is almost completely from cars and other fossil fuel motorized vehicles.
I was out in a fairly high earning suburb recently and the backyard was constantly inundated by the roar of a not so nearby highway.
Like, what exactly do you think people do to make noise?
Counter example: Europe, Japan. It's perfectly possible for a city to grow denser of people without growing denser of cars.
My inner city neighborhood is quite calm and quiet, because the city has decent public transit with three different modes within 3 minutes walk (besides decent biking infra).
When you build the city densely and don't give away free parking anywhere, it makes people not bother with driving very much. There's no place to park here, except for a few very expensive private lots that probably aren't close to where you want to go. There's no street parking. Renting a parking space at your apartment is very, very expensive (because they could be using that for something else that makes more profit instead, like more apartments or a convenience or grocery store). And you're not even allowed to own a car here unless you can prove to the police that you have a place to park it: they'll even come with a measuring tape to be sure that particular model of car will fit.
Closer to your home, maybe you should visit Amsterdam, because you've obviously never been there. There's lots of people living there without a car, and the amount of car traffic in the city center is quite low.
But living in these car-free zones is at least double as expensive as outside (and the more central, the easier it is to live car-free, the more expensive it is). It is also totally unrealistic to live there with a family, and if you want a job in center of Brussels and live in Mechelen (for example), you need a car. Train is barely doable and only if your employer is dead center brussels (e.g. Diegem, where "the internet lives", is not realistically reachable)
It's a bold theory but not one I want to try out in practice.