Yes, and these factories are many, and are not concentrated in one place, because shipping cement is expensive. It’s the same with aggregate: not everyone has sand in their backyard, but there typically is good amount of suitable sand within a few dozen miles.
There's actually plenty of drama around sand for concrete. There's talks about 'sand mafias' in India. And Malaysia has banned exporting sand to Singapore.
Similar stuff has happened in Germany, in fairly recent times. You could make your own cement, no problem. But good luck trying to unload it anywhere in Germany without paying a fee to certain individuals.
