Reason is simple : All our trailers are universal. We don't have dedicated trailer to each boat. A trailer is made for maximum indicated weight and average lenght. For exemple, my trailer is made for 2500kg boat from 5m to 7m. Means a 5m boat will look like to small for that trailer, 6m will look perfect and 7m too long.
Anyway you focus on a real problem here in Europe : Trailers are 30 years in late comparing USA. And it will not change till many years IMO.

I went back from the boat, I visit it because alot of rain last night. I started it, ok it fires after 2 tries. It runs good at idle, but takes a very long time before I can rise RPM. When I accelerate, the engine clogged.
Problem of choke ? It's an electrical choke on my carburetor