Also not a lawyer, but I think it mostly has to do with commercial use. Filming people at Disney for your Instagram followers is different from making a feature film and turning everyone standing around on a busy street into uncredited extras.

This particular site is with respect to Canada, but I'm pretty sure the same basic idea applies everywhere:

"When publishing photos for commercial purposes: You need the permission of every identifiable model in the photo, even if the photo was taken in a public space. For example, if a photo has 10 identifiable models in the photo, you would require a model release for each of them."

https://www.lawdepot.ca/law-library/faq/model-and-entertainm...