Think about the amount of times pre-VAR that the linesman put his flag up incorrectly and stopped play when he should have kept it down (for something marginal lets say) vs the amount of times with VAR that they've let play continue and something happened as a result (a goal, a corner, a penalty, a foul, etc) and it turned out (following a review) that he should have put the flag up right then and there, and they end up having to "erase" a whole sequence that incorrectly played out.
Lets face it, the former (pre-VAR the lino putting his flag up incorrectly and stopping play) happened very rarely. The latter (VAR linos keeping their flag down and letting play continue fraudulently) doesn't just happen far more regularly than the rare premature incorrect flagging without VAR, but if we're honest, it happens almost every time there's an offsides nowadays.
So they've taken something that maybe happened once in a blue moon and we could certainly live with, and we're replaced that ith something else that's wrong (and even more annoying in some ways) that happens almost every time there's an offside.