By "very high", do you mean 100%? Because that's what happens.Probably because the VAR crew are not going to tell the ref to come to the screen and check, if they haven't seen something that they are pretty sure is a penalty. If they see nothing, they won't call the ref over. So, the percentage of penalties given after the ref has been told to come to the screen is always going to be very high.
If you are using VAR, offside is binary. We might hate it's application but it is either offside or not.
Penalties can be very obvious, and they can be very subjective. The opinion of the video ref is not worth more than the ref, once the ref has seen a replay. And yet in practise the video team decide.