How so? This is not at all intuitive to me, and I would argue the opposite.
CC-BY-SA ensures that republishing of the material happens only in freely accessible work, which in the long-run advances science. I think science is greatly held back by closed-access journals.
And no one is preventing people from citing CC-BY-SA work in closed-access articles, or using it under any use considered fair use. They just can’t republish it.
All CC-BY-SA does is prevent people from directly republishing the full material. The data itself can always be used freely.
Data is not copyrightable (i.e. the pieces of data themselves, the direct information), at least not under US and EU law. The copyright is only for the observation itself, including the text of it, and the photos. And if it’s published on a website (as it is with iNaturalist), it can easily be cited by a link. iNat has good and simple permanent URL schemes to make this stuff really easy to cite and link to. And quotes are protected under fair use, so someone could easily reference a small excerpt, legally, where relevant.
I see zero need for a less restrictive license than CC-BY-SA, for “scientific” purposes. If I am wrong, please by all means explain how and why.