I have wondered about this issue too, it’s hard to understand. I have read the Bible looking for answers, and I think there is more than one reason this happens, I think it varies by the situation, and we don’t always know the particular reason, but there is always a reason why.
Many of the explanations you listed are not supported by the Bible; I am ashamed to admit that many “Christians” don’t read their own Bible. I hope that you won’t totally reject God because of the hypocrites. I encourage you to look in the word and make up your mind yourself.
"They were man's doing". Man may not directly cause this, but we live in fallen, cursed world because of mans sins. Everything dies and decays because of this, including our DNA.
"He wanted some to be like this" No He doesn't. Lamentations 3:33 "For He does not willingly bring affliction or grief to the children of men." Ezekiel 18:32 "For I take no pleasure in the death of anyone, declares the Sovereign LORD. Repent and live!"
"Its a test. He wants us to learn from them." I do not remember reading anything in the word to suggest or deny this.
"He punishes a certain few." It is not because of that. John 9:2-3 "2 His disciples asked him, "Rabbi, who sinned, this man or his parents, that he was born blind?" 3"Neither this man nor his parents sinned," said Jesus, "but this happened so that the work of God might be displayed in his life."
Here we have a specific reason this happened in this man’s life, “so that work of God might be displayed in his life". This would of course glorify God, but it could also lead to the salvation of many people. I can imagine the man excitedly telling everyone he saw about Jesus and what He did for him. The word would spread, and many would be healed and saved who otherwise wouldn’t have been had the man been born able to see.
Luke 13:1-3 "1Now there were some present at that time who told Jesus about the Galileans whose blood Pilate had mixed with their sacrifices. 2 Jesus answered, "Do you think that these Galileans were worse sinners than all the other Galileans because they suffered this way? 3I tell you, no! But unless you repent, you too will all perish." Another example that this does not happen because of punishment.
"Satan (Or any other evil being) has done this" Satan and the demons are probably one reason this happens, but you are right about this being a cop out. They are finite beings; they are not responsible for every single evil thing that happens.