This is a good point and I think it is part of the problem. I think the checked box reduces the license choices to something that looks like a ‘yes/no’ decision when it isn’t. There are nine choices and can choose differently for observation, sounds, or photos. The way it is presented makes the choice look like a ‘yes/no’ decision without telling the users what ‘no’ or unchecking actually means.
What if the default to an observation was CC0 and CC-BY-NC for photos and sounds? That way actual intellectual property has attribution but the observation is very open. It has been widely debated whether or it is even reasonable to reserve rights to an observation. https://forum.inaturalist.org/t/does-copyright-law-allow-you-to-restrict-use-of-your-observations-the-data-this-is-not-the-photos/41709