Please don't trust glassdoor! These numbers are almost all wrong.
The MBB numbers are a bit more accurate.
But the Big4 (as you note) are so far off the mark. From the data I have, the Big4 are all paid higher than what is shown here.
You have to remember that this is crowd-sourced…
So some of these data points have an N of one.
Think about how many people get hired in a year from a single city at a single company for a single role. Then think about how many might enter this salary into glassdoor. Then think how many might do so accurately).
Take all published salary numbers that are this granular with a grain of salt!