I wanted to leave an answer yesterday, but I decided to wait to see what other WTers might add, and they have pretty well covered the bases here.
I know it's frustrating and the very same thing happened to me when I was new in WikiTree. I thought, "Why in the heck is this person adding things to this profile I created YESTERDAY?" and "how did they find it?"
Well, there are reports and feeds...suggestion reports, cemetery reports, category feeds, changes feeds. As others have pointed out, there are those who follow these feeds and reports. If your nearly-new bare-bones profiles show up in these feeds, WTers will often show up to add categories, correct something, provide a short biography, or whatever. This is in the name of collaboration.
Collaboration is great, but does have a few drawbacks, especially when a well-meaning fellow WTer makes a change that isn't quite right or isn't very informing. You are free, as the PM, to revert the change or expand upon it. If you have close relatives with bare-bones profiles and they're under the limits for open profiles, I'd advise you to change their privacy level so they can't be edited by anyone but you. I usually reserve this for profiles up to about 4 degrees from myself. (Like, I'd be irked if someone tried to work on my parents, grandparents, aunts, uncles, etc. and they touch upon privacy issues with living persons.) But I'd also be open to anyone offering information or pointing out an error that exists on their profiles, and I'd perform the edit myself.
Anyway, thank you for pointing out that even though collaboration is our way of life in WT, a bit of respect should accompany it.