While I understand what you’re saying, in law school they explain why certain crimes carry the sentences that they do, and part of it is punishment, part of it is deterrence but another part is not going overboard by making the sentence the same as a worse crime, on the basis that one crime will prompt another.
In the case of something like pedophilia, the concern is that if it came with a life sentence already that the perpetrators would likely kill their victims, making it easier to cover their crime while not increasing the risk to them if they were caught.
From the perspective of the criminal, if they’ve just committed the crime that will land them up in prison for life, they may as well not let their victim go.
They go over this in criminal law in first year law school.