Police don't make the laws. Their job is only to enforce them. Police cannot ignore complaints made by citizens in their jurisdictions.
You would know better than I at what level and to what extent police forces can make decisions on how they investigate a reported crime, but I know it's not quite as simple as you're making it sound. The police do not launch a forensic investigation into every crime that is reported, and I've seen times that they will simply not get involved in a blatant crime for whatever reasons, I'm sure usually lack of resources and whatever priorities they're instructed to follow.
That said, in a sensitive case like this, I would guess the orders are probably coming down from pretty high. And I guess it's the politically safer move to follow the letter of the law, no matter how much more damaging it might be to everyone involved.
Who's the final say in how aggressive an investigation becomes? The DA? Yes, the laws need to be addressed to avoid this sort of thing, but I'm pretty sure a voice of reason somewhere up the chain of command could help a lot at the moment.
It would be a real shame if you really believe this. It's way off base.
I think there's a lot wrong in these cases, and probably none or almost none of the fault lies with police officers. After following it some more, I probably place the most blame with the school administrators and the DA. The DA is now sounding more threatening about the possibility of these kids ending up on the sex offenders list and encouraging kids to surrender their phones.
It's insanity. It does not resonate with me that this is all coming from some noble, though misguided, attempt at justice. At best it's extreme cowardice and no one's willing to be a voice of reason. At worst (and I think more likely) there are adults who feel abnormally compelled to have control over the sex lives of the young people in their charge, so much so that they're willing to fuck up the lives of those kids for doing exactly what socially healthy kids do at that age.