Ask CEMEX if you want something official. But here's the logic as I see it.

The plant has never been loved in S.C. except by the financial people at the County (it was one of it not the biggest non-government employer and taxpayer in the County) and of course by the people working there (much better wages than farm work and feeding the tourists). CrVI and other nasties were discovered in plant emissions just about the time that the CO2 crowd started jumping on the cement industry in general (portland cement production is, after all, a high CO2 emitter simply because of the character of the cement-making process - look it up on the web). Faced with an unloved facility that was going to have to shut down anyway for lots of expensive work to meet air quality and GHG standards, CEMEX apparently chose to move production elsewhere and closed Davenport. They are after all a big company with cement plants all over the US and the world - no need to get into a fight they couldn't win. If you read the various stories on the web sites kicked out by some simple web searches, they had an underutilized plant in SoCal at the time that could easily pick up the production lost by closing Davenport. Simple decision, really.

And consider this a challenge - learn how the Internet and the WWWeb works, and what a search engine is; all of this information is available with a few minutes' work. Find it. I didn't invent it. You might find something that makes you think, and that the rest of us might like to discuss.