same for Europeans in America, we would think all your bike lanes are forbidden for bikes

your defaultism is showing. In fact most of the world uses a white sign with red border to mean a prohibition.

and in fact children need to be taught what traffic signs mean all over the world, they don’t magically know it

Neither is more intuitive, it’s just what you’re used to, culturally. Europeans could equally go to America, see a white sign with black symbol and red border and remark upon learning that it indicates a bike lane ‘That’s just not intuitive’.