It does seem like swimming pools in Iceland are a bit different than the U.S., being geothermally heated. That answered my first question, which was "wouldn't it be too cold to swim for most of the year?" and may also offer an explanation for why they become community hubs: a place to be outside during winter without freezing to death. Just a guess on my part; would love to visit Iceland but haven't yet.
We have plenty of community pools in the U.S. (about 309k of them, according to a quick Google search), but the vast majority are private. We had a swimming pool at my house growing up (I consider it a miracle, since we were fairly poor), but I also spent a lot of time at the community pool.
Growing up in a hot climate, our pools were never heated, geothermally or otherwise, and served mainly as a way to cool down in the 10000 degree heat. That may be partly why there are so many private ones in the U.S.: you would jump in them to cool down, then after a few minutes you'd get out and go play somewhere else until you got hot again.
Oh, the other purpose for private pools is teenage skinny dipping, which you wouldn't do in a community hub (I assume).