Being dutch I think that the roads that share bikes and cars in the Netherlands are actually not by design but by necessity. Especially in Amsterdam where there simply is not enough space. If you look in rural areas if there is room, they are always seperated. In the cases where there is no room, the buildings and/or streets are usually historically protected as monuments and will not be demolish-able to make more room.
I'm not sure that's true. I've read articles about how they intentionally create shared roads because it makes both bikes and cars more careful, similar to the initiative of removing signs and lights in traffic (which, counter-intuitively, is often safer).
Plus, I personally recall separated bike lanes being converted to shared lanes.
