I think this is mostly due to insects’ inherent lack of identifiability based on photos. I expect you’d find that in general, on a largely photo-based platform like inat, the smaller the organisms, the harder they are to get identifiable images of, and the fewer of them can be identified. Rotifers are only at 11% RG, and it’s not for lack of experts looking at them. They’re just not identifiable from the average photo. Same with diatoms- 11% RG despite some really active identifiers reviewing them. Segmented worms are at 17%. Spiders are at 45%. Honestly most groups besides vertebrates and charismatic plants are doing worse than insects as far as RG percentage goes.
There are so many insects without names, with unresolved taxonomy, with differences only visible once dissected, etc. that frankly I’m impressed we’re at over 50% RG. Sure, we have fewer identifiers for smaller organisms, but even when you get the world’s expert looking at some of these groups, they won’t be able to put names on even the best quality of photos.
One of my favorite stories was a moth collector who collected 100s of Coleophora in his suburban yard and sent them to the world’s expert to be dissected. They appeared to represent about 7 morphospecies, but upon dissection, it turned out there were dozens of cryptic species in the sample, and of all of them only about a fifth of them had published names. And this is in the Chicago suburbs in the most over-sampled country in the world.
The point is of course more identifiers is good, and of course better quality photos are good… but there’s an inherent “ceiling” to how many inat insect records can ever get IDs, and the smaller the organisms, the more of an issue this is going to be. If you want to see a truly ubiquitous taxon with a lack of many identifiers, look at grasses- only 46% RG despite us standing on them most of the time we’re observing anything else.