The article notes that even just the dam in the Gibraltar Strait (ignoring the others) would have required more concrete than existed in the entire world at the time. I think that single reason is enough.
But if you're going to take the words and sentence to refer to reasons... list the reasons. Or, don't refer to them and write about something else.
The entire post felt like "We're going to go over {X}. So here are a bunch of things that are {not X}."
The article notes that even just the dam in the Gibraltar Strait (ignoring the others) would have required more concrete than existed in the entire world at the time. I think that single reason is enough.