Suppose there's a medieval profile I'd like to keep an eye on.
If it's orphaned, I can adopt it and unadopt it, and now I'm on the TL and the profile is on my Watchlist.
But if there's a PM, I have to go through the PM. I can edit the profile, change the parents, change the spouses, rewrite the bio, but I can't just watch.
If anybody bothered, the nuisance involved for PMs would be ridiculous. The only reason it isn't is because nobody bothers.