Because when the top people presiding over sex trafficking cases look in the mirror, they find 14 year old girls attractive too.

Because money and power are more important to people making decisions than doing things for the betterment of society.

Sadly the best people to lead are usually people who don't want positions of power like that.

Not that anyone in the "royal" family did literally anything to get where they are...

Rape cases are notoriously difficult to prove, even if the victim goes to the police immediately and there's physical evidence taken.

First of all, the supposed rapist can say "There was no rape". At times, the physical evidence can make that seem unlikely. In particular if there's evidence of violence and there's semen, then it's easy to believe that violence + sex = rape. But, if either of those is missing it's hard to prove that a rape even occurred.

Second, the supposed rapist can say "It wasn't me". Before DNA analysis it was hard to prove who was at the scene. These days, if there's semen at the scene at least you can say that a certain man was present and involved in something sexual.

Third, the supposed rapist can say "It was consensual". Given that most of the time there are only 2 witnesses, it's difficult to say which witness is lying and which is telling the truth. A jury might have a strong suspicion, but a strong suspicion isn't "reasonable doubt".

In the Epstein cases, you can at least sometimes eliminate the third objection. If the victims were underage, they couldn't consent. But, that still leaves the other two major issues. Those are the ones that really require physical evidence. And, in these cases, the evidence is long gone. So, you can't prove that a rape occurred using physical evidence, nor can you prove that a certain man was at the scene using physical evidence. What you're left with is two witnesses using their flawed memory to recall details of something that happened a decade ago.

Maybe using flight logs and emails you can prove that Andrew was on the island at the same time as a victim. Maybe you can put Andrew in a photograph with the victim, showing that he had met her at some point. That's enough to be very suspicious, but it's not enough to get a rape conviction.

Now, you said "child sex trafficking" not rape. But, if anything, that's even harder to prove. Step 1 of proving sex trafficking is probably proving the "sex" part, and that's going to be extremely difficult a decade later without any physical evidence. As for the trafficking, you'd have to prove that certain people were moved to certain places. But, that would rely on accurate documents like flight logs listing everybody on a flight. But, we've seen that a lot of the flight logs are incomplete, or they don't name the girls on the flights.

I'm sure there are powerful people trying to slow, stall or stop any attempt to prosecute anybody for what happened. But, at the same time, even if they were putting in a massive effort, it might not be possible to actually get a conviction anymore because too much time has passed and too much of the evidence is gone.

We already knew after Jimmy Saville (a high profile celebrity, pedophile, and sexual predator who victimized hundreds - likely thousands - over a period spanning sixty years, only getting "caught" after his death when victims could speak up without fear of reprisal) that there are a large number of people in British media and government who are not only willing to turn a blind eye, but to actively assist a predator in acquiring fresh victims and crushing any investigations into them, either to avoid scandal or because someone even higher up the chain told them to. It's not surprising that the rot reaches all the way to the top.