Why UK banned Hasan Piker and Cenk Uygur from speaking

Why did the UK ban Hasan Piker and Cenk Uygur from speaking at Oxford? Arwa Mahdawi's response is, "Because on Gaza, we punish the witness, not the crime." *Banning leftwing activists from entering Britain: an illiberal move with a long history in [Britain].* The Oxford Union invited them to speak by videoconference instead. I hope they don't plan to use Zoom, because Zoom censors remote talks about political topics much as the UK government censors presencial ones.