The are competing with Epic, which has a huge presence in the VFX industry - including Unreal being used on the real-time VFX for the Mandalorian. Weta was using Unreal at one time, as well. This is likely a more strategic move to a) obtain more studio tech to integrate with Unreal to make sure they do not loose the "high ground", b)obtain people in the loop who really know about high end rendering engine tech, in which they are behind Unreal and c) make sure Weta stays well away from Epic.
This is exactly on point. Unity is behind Epic in many respects relevant to both areas of business - classic game development and the nascent gaming-tech-used-for-movie-VFX business - and this acquisition is an attempt at fixing this deficit by throwing a chunk of money at someone.