Yeah, I don't know what the correct number of car washes is to have, but I swear my city has enough for every car to wash every day with capacity left over.
A lot of it has to do with taxes. These carwashes are basically just real-estate parking. The formula is simple, buy a plot of land in an area you think will be high demand, plop a carwash on it to reduce taxes for owning that land (maybe pull in a few bucks here and there), wait for the land value to appreciate significantly, sell it for a profit to future development (or another person who thinks the land will further appreciate).
End result loads of carwashes doing nothing. Pretty sure it was the same reason mattress stores were everywhere at one point. You just need like 1 person to operate the store so paying their salary is nothing compared to the future appreciation of the land value.
Except in my town they are forcing useful businesses out and tearing down the buildings to build car washes. There probably is some advantage to holding land with something that produces some amount of money, but the fact that they are willing to tear down existing infrastructure to build them implies they are at least fairly profitable.
Yeah, I don't know what the correct number of car washes is to have, but I swear my city has enough for every car to wash every day with capacity left over.