Your wetsuit stops the water. This stops the wind.

WARM AS A 3MM WETSUIT - LESS BULK. STOPS WIND

You get cold. You buy a thicker wetsuit.

You’re warmer in the water. Still cold above water.

The cold isn’t from the water. It’s from the wind.

The Paradox – why the wetsuit fails on the surface

When you leave the water, two things happen simultaneously.

Wind hits wet neoprene and strips heat through convection — moving air continuously replacing the warm air layer your body worked to create. And evaporation accelerates from every wet surface at once — neoprene, skin, hair, gear. Each unit of water that evaporates removes a disproportionate amount of heat energy. It's called evaporative cooling. 

And on the boat or sitting on a board in the wind,  a wetsuit does almost nothing.