I'll try not to give you a beating.
First - what do they want? My guess is that they want exactly what they are now getting - they want to be heard. They want to be believed. They want the world to know the truth about this man that so many have revered for decades. They have suffered in many ways over the years after the encounter with Cosby. Maybe getting it out there, and doing the only thing they can - outing him as a creep and a rapist - can help them overcome that suffering to some degree.
You say it is strange that 17 or 19 women did not have courage enough to get a good attorney. One, I suggest you take a look at rape statistics, and see the low percentage of rapes that are actually ever reported. Two, the ones who did tell someone about it were disbelieved - one woman went to a lawyer who laughed at her. Three - when it happened to each of them individually, they did not know there were more than a dozen others who had experienced the same thing. They felt very much alone with their rape experience with this pillar of the entertainment industry. This is why I am so glad for the way this story is finally coming to light - there is safety in numbers, there are other women who say "yes, we believe you because it happened to us".
Some of these women are joining the band" - I don't know what they have to gain. Who wants the so-called 15 minutes of fame so they can describe being tricked with promises of career assistance, drugged, vomitting, waking up with semen on their bodies - woo hoo, I'm famous?? Would that make you feel famous?
IMHO
Edit to add: here's a source of rape info for you. Educate yourself.
https://www.rainn.org/statistics