Twitter is most likely feeling the pressure from the right. Both Republicans and Democrats were already talking about regulating social media. Having the President of the US banned from Twitter looks bad when they allow adversaries of the US access to Twitter. If they didn't do it, Congress would've used against them when they regulate social media. I wouldn't interpret it as anything else. Twitter is not in China and they pretty much can expect to never be in China. They have nothing to lose in locking out China.