LONG-I don't understand people's attitudes toward their pets

Backstory: We live in a neighborhood a few miles from town, but there are four neighborhoods right in a row with hundreds of houses, so I wouldn't say I live in the "country."  Also relevant, our neighborhood has no street lights, so it's pitch black after dark.

People let their dogs run around without being leashed around here, which is unfathomable to me, but I've tried to get used to it.

We ended up taking a dog in a few years ago after the owners left him wandering around for days while they were out of town. We weren't trying to take their dog, but we thought he wasn't wanted any more and I didn't want him to get run over. We offered to give him back to the owners after they got back to town, but they decided to leave him with us.  We still have him...he's doing great.

Last Saturday a dog with a collar wandered onto my neighbor's property while we were having my son's birthday party, and then followed us home. None of us had ever seen him wandering before, and had no clue where he came from. It was about to get dark, and being that he was a small dog (10-15 lbs.), we took him in for the night, which then turned into a week.

We posted his picture on the lost/found group for our area on Facebook. We posted several notices on both of our walls. I brought him to the vet to check to see if he had a microchip. He did not. I circulated his picture to a neighborhood group that I belong to via email.  No results.  No one has come looking for him either or posted a flyer.  I haven't went door to door, but it's so hot here that I can hardly stand being outside no matter what time of day it is.

I was going to make a flyer to post at each of the entrances to the neighborhoods and post them this weekend to see if I could find his owner.  People frequently ride around our neighborhood on golf carts, and tonight the dog was outside and some people on a golf cart recognized him as belonging to people a little ways down the road from us.

(Side note: The other day my husband was outside with the dog, saw a lady outside on the phone at that particular house, and the dog ran RIGHT by her into the garage. By that time, we'd had the dog for several days. She had absolutely no reaction, and my husband waited right by her for five minutes to ask about the dog.  She never acknowledged that my husband or the dog was even there, so he assumed that the dog didn't belong to her and walked back home with the dog.)

We needed to go somewhere tonight, and the people on the golf cart offered to bring him home, so we accepted.  When we returned a couple of hours later, we went to the house to make sure that the dog was theirs and that they still wanted him.  They weren't home and the dog was outside again, unleashed, so we brought him home.

I'm going to go talk to the people about the dog again tomorrow, but they have made no effort to try to find him in a week's time.  I don't understand.  He's a cute, sweet dog.  I would be frantically looking for my dog until I found him!  What do the refupeas think?