An alternative way to look at it as some professions make it easier to referee at senior levels than others. When I was in the system there were a lot of postmen at L4 or L3, they had no issues with evening games because they obviously start and finish work early. I also knew quite a few lorry drivers, it worked for them as they could manage their hours, and there were lots of teachers who can (not saying they always do) finish early. Working for a CFA or the FA is clearly going to fall into similar categories as it is unlikely they will have any issues leaving a job in sport early in order to pursue a role in the same sport.
Conversely there were very few people who worked in office jobs in the city of London, especially when you consider the very large percentage of the London population who do just that, difficult to get away from work early and you can't drive to work. I can count on one hand the number of officials I worked with in those kinds of jobs, and all of them, myself included, stepped down quite young as it was too difficult balancing refereeing and work. That might well be very different post-Covid given how much easier and acceptable it now is to work from home.
I always find it distasteful when suggestions are made that someone only got promoted because of who they knew rather than their refereeing ability. Not only is it suggesting that a CFA or the FA are effectively engaging in underhand activities, but it is also effectively saying that all the observers who observed that referee are in on it.