They don't work in every situation.
One example:
Having 100,000 people to deliver mail to in a 5 square mile radius is completely different from having 100,000 people to deliver mail to in a 50 or 100 square mile radius.
If you're USPS, the mandate is "daily delivery", irrespective of the costs involved. If you were a company, you could alter a policy to "less than xx population density, you get mail 2x or 3x a week"; over that, you get daily delivery.
Same thing with a hog or cattle farming operation; yeah, you set up 100x the density of animals in your lot, you are "more efficient", but then the waste retention can become a major problem for that density of animals, vs what it was for a smaller operation. Becomes an even worse problem when that waste issue now becomes an "externalized cost" to those living near the operations. Like a retention pond bursting during a flood and fouling all the waterways and streams in the area (or even the local water treatment facility).