Its the people that did the solicitation of girls and trained them and controlled them to do as they were told that are seriously being investigated. There's no ifs, ands or buts about that. Ghislaine Maxwell had/has the reputation of being the "madam" of the brothel. She or Epstein said "jump" and the girls were required to respond with "how high?". Andrew, as far as I know, wasn't part and parcel of the gestapo controlling the girls. As far as Andrew and Virginia Roberts and the London accusation, there is no case. Andrew didn't force her and Roberts didn't say "no" and basically consented (assuming the story is true). The crime was committed by the people that were her "handlers" that told her just how high to jump and controlled her.
Putting it into another perspective as far as the law goes, Mr. Big may have a whole posse of teenagers that break into houses and steal valuables. He, then, fences them and keeps the money with perhaps giving the posse a small "token" payment. Joe Little buys some of the stolen goods and it is discovered. Joe Little is out the money he paid for the goods as by law, he accepted stolen merchandise unaware but he didn't commit the crime of stealing and fencing stolen goods.
I believe Andrew is a Joe Little. He was perhaps aware of what was going on but he actually did not have any part in the actual coercion, grooming and controlling of what the victims were made to do. That is on Epstein and his cohorts head and its those people that the investigators are pursuing.
Andrew may still face civil lawsuits but unless any of those girls have solid proof, the case against Andrew sleeping with them will not go very far. I'm sure Epstein made absolutely sure that those girls were controlled enough that they wouldn't think of crossing him or trying to escape their bondage let alone secrete away proof of what Epstein was doing. They feared Epstein and his cohorts. Perhaps now that Epstein is dead, they'll feel a bit more at ease talking to the investigators. We'll see.