Not only would I suspect that an aluminum plant employs far more people, it is an attainable job. Presumably minimal qualifications for some menial tasks, whereas you might need a certain level of education/training to get a more prestigious and out of reach job at a datacenter.

Easier for a politician to latch onto manufacturing jobs.

AFAIK, the data center employs more people. I'm not really sure why that's the case, but neither is >1k.

I'd guess that this is also an area where the perception makes a bigger difference than the reality.

How many other jobs in the area depend on being able to get their aluminum stock orders fulfilled close by?