Not all HOAs are like this. A neighbor lent his Montana 5th wheel (which is 36' long) to a nurse for this very reason. Her HOA normally doesn't allow RVs to be parked at the home, but in this case, they had no problem with it being parked in front of her house until this all blows over. He is also paying to have the tanks pumped by a honeywagon when the time comes so she doesn't have to worry about it.
As others have mentioned, HOAs are ran by a board. If you don't like the decisions the Board is making, then show up to the meetings to express your opinion, and also vote when elections come up. I was on my own HOA board for 2 years, and I found it interesting that the biggest complainers to the management company were the people who never showed up to meetings or elections. When I was on the board, for the most part, my own feelings were not important, if the majority my neighbors wanted a rule changed or something like that, then it happened. I agreed with them most of the time. We actually made the neighborhood MORE RV friendly during my time. But we also have acre+ lots. I can see why more typical neighborhoods and townhome communities would not want people parking RVs at home.
Also as a side note, there is a whole Facebook group dedicated to people who want to help First Responders and Medical Professionals like this with their RVs. Called RVs for MDs.