Because there's "fixed" things about every place in the country that will not be changing.
For example, if you can't stand heat and humidity, you can eliminate the South. If you can't stand snow or cold winters, you can eliminate much of the Northern parts of the country. If you can't stand commie liberal bastards running everything, that's going to eliminate some places. If you can't stand conservative religious nutjobs running everything, that's going to eliminate other places.
Once you have your list, go to a big-name job site and look at the count of job postings in the last two weeks for your kind of work.
If the place has 5 listings, you better REALLY love the companies, and be ready to move if there's downsizing. If the place has one thousand job listings, you'll have your choice of employers.
From that quick search, cross off any place that doesn't fit well. That should leave you with a relatively small number of places, which you can more thoroughly research and possibly visit.