European club football operates across three tiers rather than two. The lowest was added because the structure above it had stopped serving most of the continent.
Access had narrowed at the top
As the top competition allocated more places to the strongest leagues, clubs from smaller associations increasingly exited in qualifying rounds before reaching a group stage.
The secondary competition then filled with clubs eliminated from the top tier, displacing the teams it had originally been designed for.
The result was that a champion of a small association could play several qualifying ties and finish the season with no group-stage football at all.
A third tier restores a landing place
The new competition is entered largely by clubs from associations lower in the rankings, along with those eliminated from qualifying above.
It guarantees that a substantial number of smaller clubs reach a group phase, with the fixtures, revenue and scheduling certainty that implies.
For many participants a group stage is the meaningful outcome, and the trophy is secondary to the guaranteed matches. A season of European home fixtures changes a smaller club's budget materially.
Entry criteria protect the intended field
Access lists reserve most places for clubs from lower-ranked associations, so the competition is not simply filled by the strongest leagues' surplus teams.
Higher-ranked associations receive limited entries, typically through a domestic cup or a specified league position.
Those limits are the mechanism that keeps the tier distinct rather than becoming an extension of the one above. Without them the competition would drift upward within a few seasons.
It reduced congestion in the second tier
Moving lower-ranked entrants downward gave the secondary competition a more consistent standard and a clearer identity.
That mattered commercially, since a competition with a wide gap in quality between entrants is harder to sell to broadcasters.
Winners of the third tier progress into the second the following season, which links the tiers by sporting result rather than ranking alone.
The cost is more matches in a crowded calendar
A third competition adds fixtures to a calendar already contested between domestic leagues, cups and international windows.
Clubs from smaller associations generally welcome the additional matches, since their domestic seasons are shorter and the revenue is material.
The complaint comes from those who see the tiers hardening into a hierarchy, where a club's competition is set by its national ranking rather than by what it wins.

