Tribal Laws

After constantly hearing how difficult it is to investigate individuals from reservations I wanted to know why and I wanted to know who’s making it difficult. First research result stated “the blame shift” where county prosecutors lazily cite “tribal issues” as an excuse for their lack of investigation and involvement to serve and protect. This eats away at me because if I can’t get justice or a prosecution I want answers.
Can anyone explain why an adult is allowed to leave their reservation and travel 2 hours to a US county and r— a minor but still remain protected and unable to even be warranted to make a statement to the prosecuting county. Also why is it legal to allow a detective to not investigate or even turn in a victims statement to the appropriate state authorities? Do detectives get to decide what they do and don’t want to investigate after a statement is made? If they failed to do so how is that legal? It’s like turning in your homework. If you don’t turn it in you’re gonna fail the class and have to make it up somehow or you don’t graduate. Instead he didn’t turn it in, failed his class, and still got a happy retirement. Soemthing isn’t adding up and I want explanations.