There are similar rules for parking on City streets in a large city (for Idaho its large anyway) near me. Here the limit is 12K. My understanding is the goal here is to keep anything larger than a 3500 off the street. Remembering that the people that write these rules are not exactly savy on such things as vehicle weight and capacity, it can make complience difficult. There is the law, ordinance or rule as it is written, then there is the spirit of what the law is to restrict or forbade and often the two are not the same. Depending on how old the HOA rule is I would guess they are trying to keep vehicles with dual wheels off the street.