Bonus points for figuring out the correct language to use to imply repercussions for failure to act without any actual threats. Patio11 has written about similarly worded letters with regards to debt collections and banking, and I know that there are all kinds of magic incantations in law for all kinds of transgretions.
Second, those registries are much harder to find me in than a random Facebook Marketplace ad.
Third, those registries do not advertise that I am trying to sell my property or rent it out; there is no invitation to come to my home and approach me. I have literally had people show up at my door asking why I'm there if my house is for rent. Imagine if one of those people - as is common on Facebook Marketplace - was unhinged or dangerous, or got mad when I told them the truth.
It is a direct threat to my safety in a way that the mere record of my ownership of the property wouldn't be (if it had my name on it).