Because these rapes aren't imagined. Why do Repblicans think that every woman who claims rape against a Republican politician is a liar?
The reality is that false rape accusations are rare. I believe the largest estimated percentage is that about 5-10% of them are false. That means that there's a 90% chance that an accusation against a Republican politician is true. But in many cases there's more than statistics to back this up. Let's focus on E Jean Carroll's accusation that Trump raped her, since that's presumably what brought this up. Her story is corroborated by the fact that she told people about the assault at the time. It doesn't make sense that she'd tell people a false story in the 1990s and then sit on it for twenty years. It also makes it unlikely that she's lying now because it's not just her but these other people who she told at the time. But it's more than just the people who she told at the time. There's something like 20 other women who say that Trump either raped or sexually assaulted them. It's unlikely that a woman would make false rape claims against a public figure like Trump but it's theoretically possible. But for almost two dozen women to make false claims? That's nonsense. There's no way that two dozen women "imagined" a sexual assault from Trump. Some of them are telling the truth. And we also get corroboration because it's what Trump has said that he's done. Trump has admitted on tape that he sexually assaults women.
There's this conspiracy theory that Republicans use to dismiss rape allegations against Republicans like Trump, Brett Kavanaugh, and Roy Moore. The idea is that these are all just political smears. These women are paid operatives or maybe just dedicated Democrats who made up these stories about these guys to sink them politically. That's nonsense. If this were the case then why doesn't evry Republican get hammered with this? Where were the sexual assault claims against George Bush? Or Mitt Romney? Or John McCain? Where were the sexual assault claims against Niel Gorsuch or John Roberts? Or against Republican Senate candidates liked Rick Scott and Ted Cruz locked in tight races against Democrats? There weren't any sexual assault claims against them because these guys didn't assault women.
Republicans have to accept that sometimes, not often, but sometimes, their candidates sexually assault people. And when they do assault people they have to kick them to the curb. That includes President Trump, who has assaulted at least a couple of women.