Hi Gary, and welcome to the forum.
The reasons for iNat users to add agreeing IDs on observations are many and varied, and it’s difficult to distil them all into a single simple explanation. However, this topic has featured across many forum threads with extensive discussions. You may like to browse some of these threads, e.g. here or here among many, to see what other people have to say and help understand the mindset/reasons behind adding agreeing IDs.
One important thing to note here is that users who add agreeing IDs are, in the vast majority of cases, not doing anything wrong under iNat guidelines (as you will see in some of those other threads). Unless you encounter a user prolifically adding agreeing IDs en masse and you are very sure that they doing so with some kind of bad intentions (or their IDs are clearly intentionally wrong), adding agreeing IDs is not something that should be reported.
If this is an issue with agreeing IDs being added to your own observations, e.g., you find the notifications annoying, you can turn off notifications for agreeing IDs in your profile settings.