Huh! The fastest growing states in 2018 were: Nevada, Idaho, Utah, Arizona, Florida and Washington.[1]

[1]https://www.census.gov/newsroom/press-releases/2018/estimate...

Population changes are due to more than just migration. Birth and death rates are also significant factors.

That's percentage growth, not numeric growth. So while their population increase was largely due to national migration, those migration numbers didn't need to be very high because they don't have huge populations (except Florida).

Even in FL, anecdotally I know many people who moved there from CA or CO or NY not because they disliked the place they came from, but because they were forced out by influxes of _other_ people who made more money, drove cost of living up, etc. The sentiment is basically "Florida isn't as nice, but its cheap, so we make do because we have to." The brain drain from much of the rest of the country into a few small metro areas is forcing lots of middle-income people from those areas to migrate to cheaper places, and this would seemingly skew the numbers when you're looking at overall population migration.

My theories:

ID/UT/AZ -> Lower/middle class people can no longer afford to live comfortably in California

FL/WA -> People are getting sick of the progressively longer, shittier winters in the midwest/northeast

> pro choice [...] are all desirable to the young people I know

Interestingly, unlike the other issues you've listed, pro-choice support does not vary a whole lot by age. 63% support from 18-29, 59% for 30-59, and about 57% for everyone older than that (https://www.pewforum.org/fact-sheet/public-opinion-on-aborti...) Whatever causes the difference on that issue is not due to age.