The availability of ‘subspecies’ designations should not be discontinued in iNaturalist. If one adheres to a concept of species in which species are real entities (a tenant of all modern species concepts)… the recognition of ssp is incongruous with that view.
There are many additional practical issues to recognizing subspecies in a system like iNat, the least of which (though significant) being, at what arbitrary threshold does one subspecies become another for the user or subsequent identifier… best to leave it at the species level where the ambiguity is less (because you’re dealing with real entities).
‘Subspecies’ is the outlier among the traditionally recognized taxonomic categories. Species are real, all higher taxonomic categories are natural (share a common ancestor) groups of species. ‘Subspecies’ are not even incipient species, though many like to think of them that way.
See for the latest review of the topic… Burbrink, Frank T., Brian I. Crother, Christopher M. Murray, Brian Tilston Smith, Sara Ruane, Edward A. Myers, and Robert Alexander Pyron. 2022. Empirical and philosophical problems with the subspecies rank. Ecology and Evolution ():17
https://webapps.fhsu.edu/ksHerp/bibFiles/22226.pdf