This reminds me of efforts I've been a part of to open source libraries and others bits of code at companies large and small. The reality is that most employment contracts consider the employee's considered made for hire, meaning that ownership rights, in whole or large part, are given to the employer. Publishing works carries both risk and a cost to ensure the right works are published under the appropriate terms, and expending this effort is only in the interest of the company as a means of retention (and, ironically, letting your workers display their talent can easily work against retention).

> Over 90% of the studio work I've made over my career is locked away forever

Speaking as a developer, my "locked away" rate is probably >99.9% on a line-by-line basis. Glad to see the concept artists faring better, I suppose.