Princess Mononoke is a great movie. It has a very strong pro-environmental message, but it's not really that simple. Like the main antagonist also taking in the infirm amd lepers and giving them a job and a life where others respect them and treat them with dignity, as well as having working women and the men can't give them troubles or grief.
It's also very much from Japanese Shinto point of view. Disney thought all this, a movie that was a mega hit in Japan, would be a great fit for their thing and a usual princess fairty tale largely based on just the name, which directly translates to Princess Mononoke. It also can't get a G or PG rating uncut.