This is just another instance of North Americans (I haven't really seen this in British English speakers) placing their commata not at the boundaries between clauses/phrases, but where they pause when they read the sentence out loud. You may argue with descriptivism -- that the grammatical rules have changed and this is the new normal -- but placing a comma like this has the probably unintentional effect that reading the sentence out loud now causes you to pause in yet a different place.