It looks to me like Traynor understood that the follow-backs enabled the DMs, but resisted changing his behavior (at first) to not let the troll win. If the follow-backs sometimes led to nice exchanges with new friends, it's reasonable to hope the troll would tire, or that handling via unfollow/Twitter-reporting would be enough, before going full "shields up".

The way Traynor describes it, after he eventually went fully private on Twitter, the harassment moved to other forums.