I really need an answer why for this one. Is it to make those watches artificially obsolete?
Why not swimming?
As written above, and in the other threads where you posted - the PR feature needs to be supported by the firmware of the watch, and unfortunatelly it is not the case for Instinct. Have a look at the list of compatible devices at: https://support.garmin.com/en-IE/?faq=O8rHgFa3iB2HpErPIxL4v5
I have been confused by this for over a year as well. Now I see that Instinct does not support this in spite of it being able to track all my pool swims. This seems like a very easy add-on since the information is there and being done for steps, rides, and runs.