I think another issue, specifically regarding NHL mask paint jobs, is that they are one of the primary pieces of marketing the NHL uses to promote goalies. Marketing players are often about showing off gear. Especially with goalies, and especially with the masks.
As a young, impressionable goalie growing up around Toronto in the early 90's, Felix Potvin was a hero to me. And that mask was a huge piece in marketing Potvin, and definitely left an impression of "Wow, I want to be just like Felix Potvin when I grow up". I emulated Potvin's style, I got gear that looked as close to his stuff as possible. But the dream was to one day have the same mask as him.
So once I was old enough to afford a custom paint job, of course the first thing I wanted to do was fulfill that childhood dream.
I'm curious what (if any) arrangement there is with mask artists have with their designs being so heavily used in NHL marketing. Because for Potvin, I'd say that the mask design was much more iconic of his "brand" than the heavily tradmarked and protected Toronto Maple Leaf logo.