Maybe they feel that by limiting an edition, that somehow the art will be better. Keep in mind that Rembrandt, perhaps the greatest etcher of all time, did not edition his etchings. Ansel Adams, Americas premiere photographer, did not edition his photographs. Don't get me wrong, I'm not advocating that artist should not edition their work. I'm just saying that the decision of editioning should be left totally up to the artist .
Every artist has different marketing strategies.
Some prefer small, more exclusive editions that would allow them to place a higher value on each piece. Other artists might prefer an open, or unlimited edition in order to keep their prices more affordable. Legitimate hand-made prints have a natural limitation in the size of the edition. When the image on the plate or stone starts to deteriorate, the edition stops. Reproductions don't require this aesthetic judgment.