And in Roman times, concrete was laid in lifts like how foundation soil is handled today. Yeah, it's more effort than just pouring a thick soup into a vibratin

And in Roman times, concrete was laid in lifts like how foundation soil is handled today. Yeah, it's more effort than just pouring a thick soup into a vibrating mould, but e.g. precast slabs could handle a non-pourable paste. The side effect of rapid hardening would also be rather easy to handle and even allows shorter mould cycle times (and thus afford more expensive moulds). Another example would be railroad ties that could compression-mould. Those are produced in the millions per year.