My neighbors have converted their garage into living space and have between 5-7 cars outside every evening. I sure wish our HOA would do something but they HOA rules don’t give them the same say. HOAs can be good, can be bad. They do serve a purpose if not misused.
You do have remedies besides your HOA when dealing with potential violations.
If you live in a town or city with a housing code they most likely are in violation especially if the converted space is now a sleeping area. By code living space is required to have a certain amount of square-footage, light, and ventilation, and for sleeping areas egress.
There may also be a local ordinance regarding the number of vehicles that can be parked in a SFR zone. So it would not hurt to contact the zoning department.