I'm watching the 'Sunderland till I die' documentary on Netflix.
Crowds of over 30,000 people are known to watch Div3 games, when supporter expectations are high. This is for clubs based in cities with populations of less than 300k.
The only side to average that (33k)was Sunderland (an old EPL, Div1 team)who have just been promoted to the Championship (old div2), Only 3 clubs in League1,(old div 3), average over 20k. But the League average is 10k. Thus many average much less.
I note that the English Championship (Div2) is the most attended 2nd tier of any sport in the world, at around 17500.
English population 57mil (UK 68mil)
Spanish La Liga ave 23k Spanish pop.47mil
Italian Serie A ave 18300 Italian Pop, 59mil
French Ligue 1 ave 20,900 French pop, 65mil
Its clearly TV revenues & sponsorships which keeps most clubs afloat in Europe. The 2nd, 3rd tier soccer in places the game dominates tend to live much more hand to mouth, hoping to fluke a promotion. History is littered with clubs who tried to buy success to get to the top money division, failed & went bust.
Not sure how divisions here would survive the realities we see overseas.