Puzzled About "Cat Found" Notices

I write this blog using social media...Google's Blogger...posting my articles on it as well as putting a link to them on another social media site, Facebook.  I also have a Twitter account, although my use of it is more to get information than to express myself.  A few months ago a co-worker told me of another social media site, NextDoor.com, in which the user can communicate over it with others in his or her own immediate neighborhood.  Although I've never posted anything on it, I receive regular postings from others on my cellphone app.  Among these are postings from folks who either lost a pet or found one.  I understand how someone would want to put neighbors on the watch for their lost dog or cat, and I can see a good Samaritan holding a stray dog and posting about it, in hopes of reuniting it with its owner.  But what about the posts I occasionally see about someone who has "found" a cat?

In my subdivision, cats are everywhere running free, in their own yards and others', crossing the street (or boldly lying in the middle of them), jumping fences...pretty much free spirits with their "territory" being the neighborhood itself.  On the other hand, if someone notices a dog walking around loose without its "human" in sight, then it's a major crisis that urgently needs rectification.  I understand the difference: cats, unless rabid, are not going to chase people down and attack them while many dogs will do just that.  If I were to pick up, retain, and advertise  "CAT FOUND" with every unrestrained cat I saw while driving or running through my neighborhood, I wouldn't have much time to do anything else...plus, I'm sure I'd end up with a lot of pissed-off neighbors!  So I ask, how does one see a stray cat and decide to advertise it as "found"?  Now I can see somebody reading another's plea about their own lost cat and, using the animal's description, find it on the streets or in their own yard...and then directly contact the owner.  But I'm not talking about this here.  I plead ignorance on this subject and am puzzled.  Oh ye who are more enlightened, please educate me...