> Licensed under the CC BY-NC-SA 4.0 license

Seems fine to me. If you want to develop something commercial you'd roll your own anyway. Nothing else is restricted by this license.

Consider artists. There's a tremendous potential in using technology like this in art, and preventing someone from selling their works will often put them off of using it at all.

What does the license of the product have to do with the output of the product? You can use GIMP and GCC commercially, for example and libraries used with GCC often have runtime exemptions for their output

Because this tool is licensed non-commercial. Using it for art that you sell would be a commercial use, and a violation of the license.

Hmmmm. Does the licence of the tool affect the output from the tool? Photoshop is propriety but Adobe doesn't have to explicitly grant me rights to the work I create with it.

Usually no, unless say, the tool put some part of itself in the output.

The license of GCC doesn't affect the license of your binaries.

The license of python doesn't affect the license of your software.

etc.

You only need a license for the copyright though, in the worst case you waive your right to distribute your derivative code if it has been used for commercial applications (which would be a weird interpretation, but I can't find a precise explanation what the 'non-commercial' license covers).

Contrary to modern software developers, artists are used to the notion that tools developed by other people are worthy of some kind of compensation, even if found on some flea market.

Certainly, but do you see where you can buy a commercial license for this? I don't.