The golden age of Trailer Boating was the 1950's. Prior to that most either had a dock because the boat was a big cruiser, or you threw it on top of your car. A 14 footer with a 10 HP OB was very common.
My Dad docked his boat in the Niagara River, in front of what is now an Interstate Highway. Back then, U-Haul dealers rented boat trailers too, so Grandpa would clamp a bumper hitch on his old Plymouth and haul the boat back and forth to Buffalo twice a year.
When the Greatest Generation came back from the war many wanted boats. Now they were starting families and a 16 or 18 footer with a 50 HP OB was the new norm. Full size cars (Chevy Impala, Ford Galaxie, et. al.) were still quite capable of towing. The only people that had pickups were farmers and construction workers. Who wanted a noisy uncomfortable ride?
I only know about the boat ramps in my area. There are more of them now, but they have always been hard surface and well maintained.
My first trailer boat was a wooden 16 footer with an Evinrude 40 HP Lark, and a single axle all roller Holsclaw trailer. Total weight 1217 pounds. I pulled it with a 1961 Mercury Comet, equipped with a 144 CID 85 HP L6 and a 3 spd column shift. It got me wherever i wanted to go, and it even got me back.