A few years ago I worked at one of the big sports data providers, and did a huge analysis of ref stats over the past 20 years. The most shocking thing wasn't the awarding of pens, but how many fouls it took to earn a yellow card, and how much it varied per team for a single ref.
From memory, as an example Webb took 12 fouls per yellow given to Man U players, but fewer than 4 for LFC ones, across their entire career.