Because yes, she made a mistake and a pretty big one at that.
BUT
She is just 22 and obviously quite immature. He is a 41 year old married father of two kids. He is a relative unknown so a few months down the line, he will disappear from public view whereas she is very famous and she will be scrutinized a lot more for a lot longer.
I know she's done a bad thing but would you want to be judged forever on the actions of your 22 year old self?