Since all have rebelled against God and sinned the better question is why does God save anyone?
“For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. - Romans 1:18-20
If all are guilty and none without excuse why save any?
And would it be fair to give a Hitler or a Stalin or a Mao the delights of heaven and a relationship with God? Did none of their choices to do evil count against them? Would that be the act of a just God? If no, then you recognize the need for a fair judge at the end of time and are now, here, just questioning the fairness of God and saying you don’t trust him to do the job properly.
The answer to why he saves his people is, as always, love.
If the Bible is too be believed (which it's not) that's exactly what he's done. Most of the Nazis were Christians while Anne Frank was a Jew. According to your religion that means Anne Frank is right now burning in hell while the guards at her camp are now enjoying the "delights of heaven and a relationship with God". The same with the Khmer Rouge who have in recent years converted to Christianity and their victims who were mostly Buddhist.