As a background watcher of more true crime than I'd like to have watched, you're completely right. In addition, the investigations the police do are often unbelievably terrible and have at times led to decades of the wrong people in jail or under suspicion because they're racist, xenophobic, or just plain lazy and bad at their jobs.

I watched one that I found particularly sickening where they spent lots of time investigating the dad of the victim and coersing a confession out of him when the paroled, actual perpetrator left a shoe with his name on it at the scene of the crime, and the victim's young brother said that his dad didn't do it and saw someone else take his sister.

https://en.wikipedia.org/wiki/Murder_of_Riley_Fox

In Oklahoma in particular.

If it looks like a suicide and the victom is either poor or a minority, coroners aren't going to expend much effort. And that's just the laziness part. If the powerful are also involved, it's even worse.