God smote him. It is generally understood that if god killed you in anger, he wasn't inviting you home for tea and biscuits.
Brakeman. There were specific rules about how to transport the ark. Everyone knew that no one could handle the ark except those who had been assigned to do so. Everyone knew what the penalty was for someone other than those Israelites assigned to transport the ark. An example would be like dad told you not to touch a high amperage 600 volt line UNDER NO CIRCUMSTANCES ,or you will die. Nowhere does the Bible read that the man went to hell nor is it even implied..
Those "specific rules" were god's rules. God created the pothole that the cart hit, god could have made the Arc float in air and not need saving, god could have made the arc out of something indestructible, god could have instantly repaired anything Uzzah did. It was god who killed Uzzah! not electricity. It was god's spite for someone coloring outside the lines, despite doing their best.
It is a clear cut example of god being a shitty vengeful bastard. It is an example of god not caring what is in a man's heart, but of following arbitrary rules that god made up.
How could you argue that god would bring rule-breaker Uzzah to heaven? If god went to the trouble of killing him why would he turn around and give him him heaven? What was the point in killing him?, the only difference in that case between Uzzah and Elijah would be the blink of an eye and some gusts of wind.
Kind David was a murderer and pretty much all around evil person compared to Uzzah, yet one has a glorified lineage, and one is smitten, not by man's hand, not by nature, not by Satan's hand, but by god's hand. How is that fair and just?