I have a casual interest in millipedes and have spent a decent amount of time identifying them. Last winter I went through and identified all the Needs ID millipedes in Ontario. I’ve also spent some time correcting IDs of the Narceus americanus complex. We corrected a bunch with an automatic taxon change once (which works with reverting N. americanus since there shouldn’t be any observations to species) but to be fair it is not how the system is supposed to be used and it hasn’t been done again. But the inaccurate “common knowledge” around this species is entrenched enough that it’s exhausting to keep up with.
Millipedes are challenging because they’re very common and easy to find and take bad-quality photographs of, and there are several very common species worldwide (particularly in Julidae), but they’re challenging to ID and the features used are miniscule. Many species require dissection as well.
And we don’t entirely know which species exist where; they’re understudied enough that specialists are hesitant to confirm things because there may be unknown related species around.
So most observations can’t go to species, often not beyond family. That’s really boring for both identifiers and observers. That doesn’t make them less important of course, but it’s harder to motivate people to help with them.
There aren’t many resources out there for identifying small millipedes, which is a major limiting factor for getting assistance from amateur identifiers. The only good one I know of is this one for Ohio, which only applies to a limited area: https://ohiodnr.gov/static/documents/wildlife/backyard-wildlife/Millipedes+of+Ohio+Pub+5527.pdf
If you can get out ID resources and encourage a learning community around the taxon then progress is a lot easier, e.g. what’s been done with flies here: https://www.inaturalist.org/blog/75581-identifier-profile-fly-identifiers
Also worth noting that millipedes aren’t the only taxa with these kinds of issues. There’s a big list of others here: https://forum.inaturalist.org/t/computer-vision-clean-up-archive/7281