I will bite your response with the hopes you try to keep an open mind to the response you get instead of a preconceived notion of how things work.
1. Data centers are a symbol to a much larger economic schema that impacts quality of service to the area, economic prosperity, among other areas. Minnesota can literally come to prospect business and say "Look, Google, X, Y and Z companies gave us a seal of approval that our state is tech driven, come join them in the future of technology in America" You would be surprised how 1 transaction with a big brand can help future business opportunities.
2. One data center alone does not increase land value, the combination of all the variables I list ++++ do.
3. Every employee that is paid is taxed, every equipment they purchase is taxed, every goods or services they need is taxed, land is taxed. Taxation is not just what income tax and corporate tax.
4. You shouldn't be comparing a data center to a headquarter, they are two distinct parts of a business and the economy. You will have 20 people + the contractors needed from time to time + folks that need to fly to the data center 70% of their time + other marketing, sales jobs to sell the data center services to the state economy. Is it on the same degree as a headquarter? Never, nor should it be seeing as such
5. You could divide the number of jobs by 30 and you could still break-even as a city/state without accounting for the other benefits I list (and the ones I didn't). You are also forgetting that there are other costs associated with the job that are not construction work and even within construction work, there are specialists that make more money. Always remember, just because your paycheck says you make $15 an hour, it doesn't mean that your cost is a lot higher.
6. Refer to the other points and try to think of the ones I didn't list (improved disaster readiness in the region, energy consumption cost and taxes/jobs associated with it, promises to set-up green initiatives, etc)
I hope this has helped you see a different side of the equation.