This probably was a decision that came from publishers and Valve looking for extra revenue. A donate button doesn't make them more money, which is the intent behind this.
yes, its all obviously in line with Valve's philosophy of "enabling" people to create content, as long as they get most of the profit from it
its like Dota 2, they're happy to support third party tournaments as long as the tournaments do all the work and Valve gets the majority of the profits