The issue may be the same as the City penalty incident: the PL have set too high a threshold for subjective calls, which this is.
In this instance VAR would ask the ref what he saw and if it roughly corresponds to what they've seen then they don't intervene. So if he says "I saw Jiminez, I don't think he was obstructing De Gea's view" then VAR will simply go along with it. The only way they'd likely intervene is if he hadn't noticed Jiminez in De Gea's eyeline at all.
It was (likely) the same with the City penalty. The ref says "I saw some pulling but I didn't think it was enough for a penalty", so VAR don't intervene even if they actually think it should have been a penalty.
Basically, the PL have introduced a particularly stupid version of VAR in an attempt to reduce interventions, I think.