That's why it's voluntary. They owned the property.

I actually own a home and I am a member of an HOA. It's rather restrictive. My mailbox has to be a certain color. My front door has to be a certain color. I can't have window A/C units. My grass can't be above a certain height. I can't have yard sales, etc. However, before I bought the home I was told that if I didn't join the HOA, I wouldn't be allowed to buy it. I could have just said no, but I didn't.

Imagine a different scenario. There was no HOA when I bought the house and no mention of any future plans. I bought the house without any conditions. Now, one day there is a knock on my door and someone says "You're now a member of the new HOA. If you don't like it, move."

Historically, that's more accurate of the government. Do you know the history of the states? A few people moved into an area. They homesteaded some land. Eventually, a small group of people declared that that area was a state. The owner of the land wasn't consulted. The vote wasn't unanimous. One day, an agent of the state shows up to a farm. The exchange went something like this...

Agent: Hey, there. We're starting a new state.
Farmer: That's great to hear! I'm a good neighbor and I look forward to trading with you. Good luck!
Agent: No, you don't understand. You're part of this state now and you have to pay taxes.
Farmer: What?! I didn't agree to this! This is armed robbery! You're no better than a thief!
Agent: Well, you can always move.
Farmer: Move?! I've owned this land for generations. Why should I move? This is my land.
Agent: Not anymore.