Primarily while the EPL has always brought in more money the gap has never been this wide. The revenue accelerated dramatically only starting in 2013 and increased payouts did not truly become available for transfers until the 2014 summer window. That gap between the other leagues has since become larger and larger.

Another significant factor is how those payouts are distributed. The EPL has historically paid out its revenue far more evenly than other leagues. La Liga is the worst offender. Up until recently a massive portion of the league revenue was funneled to Real Madrid and Barcelona. This resulted in them being by far the highest earning teams even though the league total revenue was on par with Germany and Italy. As we all know the result has been complete dominance in the UCL by Real Madrid and Barcelona.

La Liga has since taken measures to more evenly distribute payouts and already Madrid and Barca are losing ground to top English teams. Bayern has owned German revenue with similar lopsided distribution although not quite as blatant and are likewise struggling to keep up with English teams. Bayern will keep up longer as they have managed their finances more efficiently but Madrid and Barca are carrying massive debt which will make it difficult to continue to keep up with exploding transfer fees and huge contracts. It will be interesting to see what happens but all this is pointing to there being a much larger number of teams in the "super club" revenue tier in european soccer and a majority of those teams will be from the EPL. Far behind us are the days when Real Madrid, Barcelona and ManU were in a league of their own. Chelsea, Liverpool, Tottenham and Man City are all right there now. Leicester, Arsenal and maybe even Wolves with their new ownership could break into that tier very soon.