The main reason is that most homicides are not the fancy middle class pre meditated murder type of crime as seen on TV but are often related to other criminal activities and with low evidence. This means that any witnesses are likely going to be within that world of not speaking to the police and any evidence in a gang killing for example, will be of low quality.

But it also matters what we mean by "solved" too.

Try watching a show called “the First 48” on A&E sometime. Their murder cases are only solved because a suspect confesses. If the suspect doesn’t confess, or lawyers up, then forget about solving it.

My own personal speculation is that TV shows have a lot to do with it. People watching TV get used to the idea of an elite crew of colorful personalities inevitably hunting down their man, and they think murder is a guaranteed jail sentence, so they murder less often. In reality, probably pretty easy to get away with murder.

Also: video games. Young men, who commit most of the murders, spend more time playing video games and therefore less time murdering.

Yup, and this doesn't even include all the disappearances that never get called homicides. You're disincentivized against calling a case a homicide if you can't bring a case—your clearance rate will drop. It also doesn't cover all the clearances which involved an innocent person pleading guilty to avoid heinous sentencing.

I read that in Mexico that number is less then 10%. https://www.animalpolitico.com/kill-murder-mexico/homicides-...