For the same reason that someone who is in a plane crash survives when hundreds of others perish or that someone who hits their head with a kitchen cabinet door drops dead from brain trauma. Was the person who survived more holy than those that perished? Was the person who died from hitting their head more evil?
Jesus answers that by saying, no. That is the nature of the world. Ecclesiastes expounds on that by saying that time and chance happen to all men and we do not know the time of our deaths.
I personally believe that Sodom and Gomorrah and the other five cities on the plains were destroyed because they posed a threat to Abraham and his decedents. Just as the people of Israel were led out of Egyptian bondage and given the land that Abraham, Isaac, and Israel claimed before their move to Egypt.
God worked to establish his people in the land he wanted them to have.
And remember that Joseph, Mary and Jesus were living in Nazareth when the men from the east came. Herod had children in Bethlehem slaughtered, but Jesus wasn’t even there at the time. Herod was just an evil man.
There is no evidence that they posed a threat to Abraham and his descendants, because the scriptures say that God had told Abraham that his descendants would go down to Egypt and spend 400 years there in bondage and afterwards be liberated (Genesis 15:13). This was before the angels went to pay Sodom a visit in Genesis chapter 19.
God altered history for Hezekiah because in the scriptures Isaiah went and prophesied to Hezekiah to get his house in order because he was about to die. Isaiah had no sooner left that Hezekiah prayed and God told Isaiah (before he had even left the courtyard) to go back and tell Hezekiah that he would live. God altered history at that point.
Lastly, Jesus was born in Bethlehem and the wise men came to ask where the child would be born who would rule over his people Israel. They were told that this child would be born in Bethlehem according to the scriptures. Herod then ordered all male boys 2 years and under in Bethlehem to be killed. Joseph was warned in a dream to flee to Egypt and he did with Mary and Jesus.
It doesn’t matter where they lived. God had warned Joseph in a dream to flee and he could have told all of those parents in Bethlehem in a dream, too, to flee to somewhere else but He didn’t.
Why alter history for King Hezekiah but not these parents and children living in Bethlehem?
I guess it is good to be king (in this case Hezekiah) as some have often said. I.E.: “It’s good to be King.”
Not so good to not be king (in this case Hezekiah) I guess...