I don't understand why they weren't arrested
Probably part of the settlement that she would not press charges.
Maybe, but if she was at the hospital that day talking to police I would think they'd get arrested
High profile stars? No way they’d be arrested the same day. You’d do an investigation to at least make sure that you could corroborate her story that she was seen with them that evening. You’d probably interview them also, and given that they’re professional basketball players that frequently travel out of state and can afford good lawyers, even setting up that interview could take a while.
At some point early in the process she retained a lawyer, and they decided going through a civil suit would be the better option for her. And, yes, she agreed to not press charges while they admitted to no wrongdoing, and the case was closed.