> People still rarely do this in music, as holding up industry secrets is deemed more important than fostering a community of personal growth.

This is absolutely not the reason and it's surprising to read this opinion stated as a fact.

First of all, not revealing multi-tracks doesn't prevent personal growth. Human ear is pretty good at discerning individual elements of a mix. It's all in the final product. If you can't learn from it or can't hear something, either it's an unimportant part of the mix, your ear is not good enough yet to distill any meaningful information from the balances of the mix in question, or it's just not a good mix.

Secondly, multi-tracks are not the source code. Putting it in relevant terms, it's just the assets. What's important are processes and artistic decisions made while processing them and combining them in their final form.

Not revealing stems/multi-tracks is not a matter of gatekeeping, it's a safety measure to prevent unauthorized use of individual composition elements and creation of "alternative" mixes which break artistic integrity of the piece.

Music is art (at least a considerable portion of it), and and artist needs as much control over the final product as possible. Mixing is a part of it.