I agree, if they are buying, they had to get a copy of the rules.
Now......sometimes HOA rules and CC& R's can be out of date, and the HOA doesn't want to spend the money to update them, so everyone just ignores those rules.
A coworker is Asian and was shocked to discover her CC&R's ban Asians from living there "unless they are domestic help". Those rules were drafted in the 1930's, and the HOA just decided since it would be illegal to enforce that rule, and the cost of refiling the rules is so high, it will just ignore the rules.
A more modern and common rule that is illegal is one that bans the placement of TV Antennas, or satellite dishes on homes. FCC rules, that were upheld by the U.S. Supreme Court say it is illegal to ban antennas and satellite dishes. The only thing the HOA can do is establish rules for how they are attached to houses.