Up until just a few decades ago the hardest thing for people to get was food, not housing as it is (for most of the people on Lemmy) today.

Because of this, being fat was seen in various societies as a sign of wealth or beauty, sometimes both. As late as a hundred years ago the US and Great Britain had “fat man societies”. Here’s an article on that:

https://www.npr.org/sections/thesalt/2016/03/07/469571114/the-forgotten-history-of-fat-men-s-clubs

We can’t really know why the “fertility idol” sculptures look that way, but if you’re an early human spending your life going through cycles of feast and famine as you follow prey animals sticking around with the fat person you ran into was a good way to stay alive.