[spacebacon]

In short it seems like a combination of high labor cost, high corrosion risk (concrete chips and salt water erodes the rebar inside) and technological advancement (fiberglass). Also the steel shortage that birth these in the first place was short lived.

[notahacker]

Yep that. Plus the Mulberry harbours were designed specifically to be sunk to act as harbours and breakwaters, for which concrete is actually fairly well suited. We have other ways of building harbours during peacetime that don't involve sailing them across a large body of water though

[lukan]

Basically, no one would have ever started using concrete, if steel would have been more avaiable.