Hello,
I just set up a store and added a product. I set my shipping rate in my vendor dashboard : dashboard > settings > shipping
When I added my product to the cart- shipping showed. All was well.
Either your vendors do not have their shipping rates set or they do not have their store addresses set.
Please check over your vendor accounts. Look to ensure, as I mentioned in one of the posts above, that they have their store address set (they go to: pro dashboard > settings > store) and shipping (pro dashboard > settings > shipping)