But why? What are the reasons behind your thinking?
Dear Quantum,
The Chopin études as a set address three basic sets of technical problems which he saw as fundamental in piano playing: conjunct notes, disjunct notes, and double notes. For example, 10/2 would be an example of the first, 25/11 for the second, and 25/6 for the third. These are the most complex examples of each of these problems.
Each Chopin étude is monotextural, with some notable exceptions such as 25/5 and 25/10, but in general they deal with one specific problem. For this reason, it is not only the name that makes them études.
We can go through each of the 24 and know what exactly is being accomplished by each one, whereas this is not the case with the Allegro de Concert or Variations op. 2 because they are chiefly concert pieces.
There are many sections in the sonatas, ballades (especially codas), scherzi, and concerti that point to specific études, lending credence to the idea that they are not only ends in themselves, but also a means to a pianism required to render his larger conceptions.
I hope this helps you to better understand my convictions.
Best wishes,
Jean-Baptiste Morel