There are much easier ways to fix a game.
But the odd VAR 'glitch' would go relatively unnoticed because the operators (who incidentally have invested £Millions in the technology) are't going to say anything because that would be essentially admitting that the system they claimed was accurate can't be relied upon.
Say it happens 10-20 time a season, different teams, in matches that don't effect promotion/relegation/the title/CL places. Those kind of patterns are incredibly difficult to spot, and as long as they don't get too trigger happy, nobody is ever going to know. Someone being influence by a betting syndicate could do a lot of damage.