The problem is that he made threats that he cannot legally follow through on. Not only due to jurisdiction, but because the only claims that could have had even a slight chance were the ones that he admitted were true.
And even that overstates the case. The entirety of Kim's "libelous" accusations are that Evans told her that he had been seeing prostitutes, and that he had traveled to Thailand for sex. Even assuming she had no digital evidence of these claims, she had at least one witness (Evans admits that Producer Bob was on the same call where he told them). Also, she could have pointed out that he confessed to more shocking behavior in his own book. How much reputational damage could her reddit post have caused, for a guy who had already told everyone that he was a creep and a pervert?