Let's be absolutely clear here. TV income rules European football, period. TV money, sponsorship income, and matchday income are the three pillars of revenue for these clubs, and sponsorship income is heavily, heavily correlated with TV money.
The kinds of clubs we're talking about here, the Benficas, the Basel's, the Ajax's are some of the very best run clubs in the world who excel at talent development and always wisely reinvest their funds from sales. But there is no way for a domestic league in a country of 10 million people to generate the same kind of revenue as La Liga or the PL in much larger countries in languages and cultures that are globally familiar, adding even more available market to sell. Those clubs in smaller countries are in the financial position the market has dictated for them.
UEFA, through its wildly popular continental competitions COULD act as a countervailing force, structuring the competitions to make them difficult to be dominated by a handful of clubs and countries and disbursing its enormous revenues with an eye toward supporting the game everywhere.
They do the exact opposite, centralizing all the focus into the CL, ensuring safe passage to all the big brands into those big dollar games, and even having the gall to structure their prize money with a large chunk of it being dictated by the local TV market of the competitors. They emphasize and reinforce the disparity.
Corruption, greed, cowardice, there are many reasons they do it, but it's a terrible detriment to the game. The global audience is fed a steady and ever increasing dose of their glittering Juve vs. Barca type matchups and that revenue just feeds back into creating more of the same, while the heart and soul of the sport, the local interest, the match-going supporters, the community bonds, wither on the vine. It's a mistake.