I guess a lot of them didn't want to harm their career any further. For example Rosanna Arquette, a lot of actors did very well out of Pulp Fiction, it helped John Travolta etc a lot, but her career didn't pick up, there is speculation why that may be
Also, at the time a lot would have been rumours, so "big name actress A" couldn't speak out without knowing for sure others would back up her story
Some victims unfortunately feel shame, think it's their own fault, when his is the monster, not them
Reminds me of Mike Tyson years ago, some of these celebs are probably so used to some people throwing themselves at them as they want to bang a celeb, they don't expect a refusal to their advances
Recently it emerged that Carrie Fisher gave Daisy Ridley advice to be wary of ppl who just want to "have sex with Princess Leia".
Jessica Hynes as well another example, always seemed strange the lads she worked with did so well in Hollywood, now we know why she was "stuck" here.
Some ppl want to gloat they had sex with a famous, some famouses like to add notches to their bedposts.