TIME will fix this. You can’t persuade reluctant people, but over time, they will either age out or come to see the advantages of iNat. This is something that will have to emerge as iNat continues to proves its utility and as the community adjusts to its advantages and disadvantages.
Much of the natural history world is still trapped in the past. Not the 20th century, but the 19th. We are still cranking out paper field guides that are obsolete before they can be published (and then they go out of print). Most natural history web sites are awful.
Consider that iNaturalist has actually gained significance extremely rapidly. Of course there are going to be some holdouts. And in recognition of their caution, we shouldn’t assume that iNat is complete—there are things that should be addressed, there are likely problems that haven’t manifested yet, and conventions and use cases are still evolving.
Ultimately, the Network Effect, the concept that the utility of a service increases as more people uses it, is going to force people into use of iNaturalist. They will find that they are excluded from projects or don’t get as much attention, participation or utility, if they don’t use it.
iNat is rapidly becoming a criticism scientific infrastructure. I hope it’s prepared for this degree of public trust.