Because Mo's striking is primitive and quite bad and Newton's is tricky enough to make a fool out of Mo
His bad striking is usually covered up by his athleticism and the low level of his opponents who he can showboat against but when he meets a good striker he does get exposed ( Jiri, Newton, Calvacante, Mousasi who banged Mo up pretty good as examples)
His KO win over Jiri was because Jiri had a hellish fight with Nemkov where Nemkov was beating Jiri but had to quit due to exhuastion so Jiri was exhausted and damaged for his final fight against Mo whereas Mo had a super easy quarter and semi final match
Despite all that Jiri was still torching Mo on the feet until Mo landed a good counter and with Mo's power it was lights out for Jiri but if Jiri was as fresh as Mo that would have been a slaughter and Jiri would have rightfully KO'd Mo