In limited editions e.g. 50 or 100 as they know that releasing more would reduce scarcity, prices would drop and no-one would buy their art any more.

And the prints are difficult enough to duplicate without having some artistic skill. Infinitely more so then choosing Duplicate on a computer.

Artists in the signed print run business don’t generally run new runs, for the simple reason that they understand the moral contract and more importantly the economic implications: if you do reprint, the value-add of your assertions plummets.

The same artists will usually have other non-numbered or print-on-demand art.

> How is a print difficult to duplicate?

A multi-layer screen print is not trivial to replicate without the original assets for the individual layers, and material information about the inks. That’s like asking how a painting is difficult to duplicate.