The job of juries isn't to determine if a crime is serious.
Their job is to take in the evidence, deliberate on it, and come to an agreement on whether they are all certain that the defendant(s) did what is accused.
CPS agreeing to prosecute is great, but they also have the very very difficult job of proving the case so 12 people are certain, while we're under well documented shortage of barristers, not all of which prosecute, and many prosecutors aren't at a level or wanting to work on the level to take on rape cases.
I think if more people sat through rape trials (which any adult can do), they'd see why making these cases convincing is so difficult, rather than just going on the rates, many of which only give those found guilty on trial, erasing those convinced to plea guilty prior to that.
Also, remember that any stats on this will likely include so-called 'historical' rape cases - ones where it's said to have happened decades ago. I've seen cases involving events over 50 years ago. It is very hard for anyone to remember enough to be convincing on that, the evidence will be very slim, and the conclusion often reached is that something horrible happened to the victim, but left very uncertain if the person in the dock is the right perpetrator. I've seen convictions on these type, but they're very difficult.
That's also why I think the backlog impacts rape cases far more than many other crimes, and again has nothing to do with juries. Rape cases brought now if they go to trial with a defendant on bail likely won't be heard in much of the country until mid-2027 - we don't have enough barristers or judges who can do rape cases, it's strongly discouraged to do back to back rape trials for obvious reasons, and we don't have enough courts with a significant portion having been sold off in the last ten or so years. The more delays happen, the more 'I don't remember' gets heard, the harder it is to convince a jury.