Bad neighbor

I live in a townhouse-style condo. Each building is made up of four units. We each have our own driveways, garages, upstairs, downstairs, and basements, but four condos - two on each side - face each other across a larger, common driveway.  There are a total of four buildings.

I'm not a bad neighbor in the obnoxious sense. I don't bang things or blast music at odd hours. I don't have a barking dog or loud children. But I have lived here over four years, and from a lineup I could pick out ... maybe five of the people who live in those twelve units. Total. Probably tell you their first names. And I was the condo association secretary for three years.

My next door neighbor has owned her condo for about a year. Once she stopped by while looking for her cat and we introduced ourselves, but I can't remember her name. I know she has two daughters. One of my across-the-driveway neighbors is - I think - a single young woman ... but maybe her boyfriend lives with her too? Maybe he's even her husband? She or they have been here for about six months. Next door to her is another woman with a live-in boyfriend and two sons. I do know her name and her boyfriend's name, but they've lived here as long as I have.

We all wave or smile and sometimes say hi if we pass each other outside, but that's it. I have no clue who lives in the condo that shares a back wall with mine. I never formally welcomed the newcomers. Does this make me a bad person? I think about my neighborhood growing up, and we kids were out playing with the neighbor kids all the time. All of the parents knew each other, and the non-parents, too. My mom and dad still exchange Christmas cards with most of them. Were they just friendlier than me, or have times changed? If I'm guilty of being a bad neighbor, then I suppose my neighbors are just as guilty.