As to whether or not zoning laws are what prevent people from owning horses, that's not clear to me. But a law saying you can't build a bookstore or apartment on the lot doesn't seem very related.
Everyone thinks they want to "get rid of zoning" but, of course, there are "obvious" rules we would all need to follow and "of course you can't do that" ... and it quickly becomes murky as to where "zoning" begins and ends and which regulations are "legitimate" or not.
Either people can communally decide what rules they want to enact or they can't.
If they can, restricting multi-family housing is as legitimate as anything else in a democracy. Like allowing or disallowing horses. Or limits to vehicles-on-blocks-in-the-front-yard. Or ad-hoc septic systems.
How big is this community? Who decides that?
Or, at the very least, to not do anything out of the ordinary.
Hint: it's not Tokyo, which actually does have a fair number of old ugly poorly-maintained buildings scattered around random nice neighborhoods. Which is fine and not hurting anyone.
Anyway, those older, ugly, poorly-maintained buildings eventually get torn down and replaced with something better, because the land value is very high. It's much more laissez-faire than the US and property rights are much, much stronger (the idea that you should mostly be able to do what you want with your property).
Cause suburban Americans are famous busybodies. There's no way you can outdo them. They think anyone walking past their house is casing it for a robbery and will call the police and post on Nextdoor about it.
There's no space for people to have a horse.
There's plenty of places that I think everyone would call a "shack" made from old tin that's probably been around since the 50s or so, and is not really any different from a mobile home. So that exists here and people are generally OK with it.
People wouldn't disconnect from the sewer to do septic. That isn't a zoning issue, it's a public health one, and it's obviously illegal.
Honestly, none of the hypotheticals described have to do with zoning. Social pressure to do the right thing is a thing here, but not the only reason that things aren't super chaotic.
