I think its more than HI, its the entire Hilton Brands WiFi system. I stay at Hamptons, HGI, and ES, throughout the country, and 99% of them require a access code.
But your point is well taken. What is the point of the access code. Forget about crowding the lobbies, maybe its the parking lots? I know I try to find the nearest Panera Bread if I have to download a big attachment on a laptop while traveling. Thankfully Panera has no access codes.