I think the biggest reason is that trucks are less practical in Europe.

European streets are often narrower and parking spaces smaller. Many trucks that are popular in the US are so heavy that you may not be allowed to drive them with a standard license. You need a truck license, which may be valid only for a few years and have stricter standards. And due to the climate, you are more likely to have to protect the cargo from the elements, which shifts the balance towards vans. But vans are not very convenient in daily use.