Until this year there was a real imbalance in refereeing levels in the North and South. L3s in the South would mainly referee steps 3 and 4, whereas in the North it was often step 5 or even 6. Same for L4s who were step 5 vs step 6 / 7. For L3s it is a national merit pool, so far from fair that referees were operating as many as three steps apart.
Also in the South, and London / home counties areas in particular, it is quite a transitionary situation. Referees move here when they are younger but then often move away when they get older and are looking to settle down with families. I can think of several former and current EFL referees that went through promotion down here but now live elsewhere.
I think I’m right in saying that areas like London do not have an actual supply league as such, which means London referees - who get the marks - are sparsely promoted on surrounding supply leagues.
This probably has a knock-on effect on the flow of referees progressing from Level 3 and beyond, in the case of London and areas without its own supply league.