Bikinis are not out of style. People are fatter. Though I guess styles go with the girth of the customer.
You’re right that being fat has something to do with it, although the motivation is not modesty but vanity, they’re buying the ones with built in “compression,” containing essentially what was known as a girdle in the olden days. It’s a trend for which we can all be thankful.
Now, if those bloated German tourist guys would stop wearing Speedos we’d be getting somewhere, geez it’s disgusting. Europeans in general seem to wear the things for some strange reason.