The 'direct' cost - lower property taxes, for example - is offset by often having to drive further for basic stuff that you may be able to walk to or use public transport for in a larger city.
There's also a social cost - fewer human interactions - which, for some people, is actually a positive, but it's not for everyone.
Also, opportunity cost can be higher out in the country. You may simply miss out on experiencing things that you would in a city. But in a city, you might miss out on cleaner air, nicer sunsets, etc.
Though it will properly cut down on the amount of commuting people will have to do.
There are many advantages to clustering together that electronics and increased communication simply cannot replace yet (and I doubt it ever will, even video calling feels "phony" somehow).
20k is a town. 100 people is nothing.
The ability to walk down the street at 3 in the morning and see a non-trivial number of people around.
A friend was in a small town teaching for the summer, and he said "So then we went to the bar. I say the bar because there was only one." Where I live, there are 171 listed in the phone book.
It's all subjective, after all; but that's just off the top of my head.
The industrial and neolithic revolutions brought the masses together to form towns and then large cities, where as I believe with the increase of freelancing and e-jobs, along with better remote working environments, people will start to question the high cost of living within a large city.