copyright law regarding data varies a lot by jurisdiction. but beyond copyright law, there are contract laws that can protect data, and there are just social norms that offer some protection, too.
in the case of contract laws, it doesn’t look like iNaturalist actually has specific terms of use or mechanisms that would regulate people’s ability to use / reuse data, other than stipulations that the API is not to be used to do bulk downloads. however, if your data goes to GBIF, it is protected over there by GBIF’s terms of use + data user agreement and policy that requires users to log in to download data. those terms require data users to respect whatever license terms the data publishers have applied to the data.
in terms of social norms, if someone explicitly indicates that they want you to respect certain conditions such as attribution when you use their data, even if you are not legally required to do so, i would think it’s probably best to still respect whatever those wishes are.
at the end of the day though, if you’re seeking to protect IP rights, you have to consider what you’re protecting and what options you realistically have to enforce your wishes. even if you could seek recourse in the courts, would you actually go to the effort of hiring a lawyer to represent your interests in court? or if, say, someone didn’t credit you a source for data that made up a large part of their research, would that matter to you so much that you would shame them in whatever circles consume that research?