Etymology is so fascinating, particularly when the original references the word was built on have completely ceased to make sense. I'd imagine most registries in this day and age have absolutely nothing to do with a king, even in countries where a king is still a relevant concept.
I am possibly also unduly amused by the tossed in reference to racking under the list of definitions for *reg. I suppose that does have a little bit to do with kings.
That's the thing - is they're not relevant in a social day to day context.
But in many cases they are such as registering anything in government - particularly commonwealth countries.
When you register, you make a temporary transfer in title, meaning it's no longer yours.
And that's why you must meet all the standards set forth such as having insurance otherwise you get your property robbed from you - they can't take what isn't theirs otherwise it's a crime.
By registering, you made it theirs, and thus they will do what they want with it especially if there's a possible liability issue.
For example, going form point A to point B in a registered car with no insurance?
That's part of the contract when you registered it, and thus it's a liability because you're not following the rules set forth that would relieve them of liability. Impounded car.
Etymology is interesting for sure.