It's because terror organizations tend to be quite civil on Twitter, whereas political trolls tend to be...trolls. The former isn't inimical to the proper functioning of the service, whereas the latter is.
Re:Reddit is still in turmoil
by benmmurphy on Friday July 22, 2016 @09:38AM
(#12143402)
to be fair twitter probably doesn't want them on the platform but the US government has probably asked them to leave them alone
Twitter, for example, ban political trolls and populists, but tolerate terror organizations and their supporters. Like what the actual fuck...