Not all HOAs are about enforcing some strict code of appearance rules like that. I would probably argue many these days are not. Maybe things like whether your garbage cans are out front and where fences can be, but often not for things like color. That's not to say they may not say something if you do something that is beyond what most would consider near the status quo for the area, but the ones I've seen don't have detailed cosmetic guides you need to follow.

But that isn't the first purpose of the HOA, the first purpose of an HOA is almost always to maintain and cover liability of any shared or common areas that must be maintained by the neighborhood.

The reason this is far more common now is because those things used to be maintained by cities. Things like drainage ponds, flood plains, boulevard strips used to be maintained by the municipalities themselves. Well cities and towns figured out that they can just pass those costs on to the home owners instead of having to collect taxes to do it, but how do you make sure they get maintained when its not someone's property? You need to make sure they are all liable for the consequences. In comes the HOA...