Likely because in todays world all that's needed is an accusation and it's up to the accused to defend themselves against it. It sure is when accusations are made of conservatives, "I heard you used the N word while drunk at last weeks party", well, I never....yeah, well thats what I heard, the rent a mob is on it's way to your house as we speak, I'd suggest you come up with evidence of never having uttered the N word while drunk before you're cancelled.
You cant prove a negative, and it's up to her to prove she never burned her kids with a cigarette. Oh, wait a minute, she can't do that, she didn't comply with police orders and is now at room temperature.