Just because a pianist can ‘reach’ octaves and certain chords doesn’t mean that they are playing within a healthy range of motion. Muscles and joints repeatedly operating at their extremes will wear out over time, leading to pain and injury resulting from overuse.
Having a span large enough to play extended passages of octaves without a build-up of tension is especially important for any pianist that does not wish to be restricted to baroque and early classical repertoire. Excessive stretching and tension also impede musicality. This includes lack of power and control over dynamic range, rhythm and speed. Pianists who experience pain are also often reluctant to speak out! The mentality of ‘no pain, no gain’ is still persistent.
Although excellent technique is very important and can help overcome certain obstacles, a pianist with a larger hand span will advance to a higher level and will be able to play a larger repertoire than his/her small-handed counterpart, everything else being equal (including musical ability). The higher the level of difficulty of repertoire,  the more this handicap becomes apparent.
Overcoming many technical obstacles often leads a small-handed pianist to ‘work-around’ solutions which nearly always require more practice and/or produce an end result which is sub-optimal.  Pianists who now play alternatively sized keyboards have come to appreciate the far-reaching technical difficulties they used to face due to hand size, and how their previous need to focus on just ‘getting the notes’ prevents full musical expression.
The view of some that ‘hand size does not matter’ is not based on sound principles of ergonomics and biomechanics.