God allows evil for several reasons.
1. Freewill
2. To refine His Saints
3. For punishment
"that one guy was just a kid"
Look at it another way. If that kid died later rather than now, he might have committed much more sins and have a worse punishment in hell. God often takes sinner early as a form of mercy. Many times God allows sinners to stay alive as a form of punishment and also mercy. I.e Giving them time to repent or allowing them to add sin to sin as a punishment for their sins.
Evil abounds because most people do not repent and follow God.
I understand all that. I wasn't trying to get into a big discussion on the youngster who died in the implosion of the sub. But I appreciate you making this point because a lot of people.. I've met people on forums who bewail everything "bad" that God allows. A lot of times they are in grief because someone they loved died "too early." I tell them things such as what you mention here. But again, a lot of secular forums are hostile to Catholics.. Understatement.
The loss of the lives in the sub also sent a message, received or not, to the survivors, the loved ones. I mean, death always makes people think of the next life.
As it says somewhere in Scripture: Think of death and you will not sin.
Looks like people aren't thinking about it much these days.. otherwise, why all this hideous sin (grooming.. sɛҳuąƖizing children.. pushing for abortion to the 9th month... transgendering, the lawlessness at the border [broken federal laws]... etc)