If you believe you are an isolated incident, it may be harder to come forth and level charges. You are working against whatever reputation, money and prestige that person may have. Once there is an indication that it is not an isolated incident, and you may be able to face it in unity with someone else, that may spur you to take the leap. Even then, you may hold back with the hope that the other person may succeed and you don't need to involve yourself.

In this case, we had Trump attempting to cast the video as entirely just talk, with no action involved. I think it's entirely within expectations that someone that had experienced this behavior may have had their hopes of justice which had risen during this incident dashed (given there wasn't an actual person to respond, just the video), and decided that was the straw that broke the camels back.

We saw this with Cosby as well, or do you think he's innocent? If you think he's not innocent, how do you explain all the people that only really spoke up loudly after the main report? We see this all the time. Coming forward is a risk, and until the perceived risk is lowered, you may not see many (or any people).

Now, it is possible that the people coming forward are making it all up, as it's always a possibility, but given the video and Trump's very affirmative statements on the video (of a 60 year old man, mind you. He should have learned long ago what is and is not okay with regard to sexual advances), I think it's far more likely that at least some of the women coming forward are telling the truth.