SD snd Nebraska are more religious and have large Native American populations.
Both states have lower costs of living, particularly for housing, compared to more urbanized or coastal states. This makes it easier for families to afford children, with experts linking increased housing availability directly to higher birth rates.
And, afaik, they have a commitment to law and order, and pro-family policies (e.g., lower taxes and fewer restrictions on family life)
But Utah
Note that none of the states listed as being above average are Democrat run. Having Native American population is a factor as well. Alaska has about 22% of its population in that category. Interestingly, Oklahoma is not listed even though it had a high Native American population, a low cost of living, and a high level of religious adherents.