Here's a "slice" of what may be going on.
The days of spitting watermelon seeds across the front lawn or carving the hollowed-out rind into Noah's Ark are long gone. So are those great big, triangular slices. According to the NY Times, farmers are increasingly breeding seedless, smaller melons with dense fruit.
The article discusses University of Arkansas plant pathology professor Terry Kirkpatrick and his work popping open watermelons as his lab works to find the most durable breeds to ship to urban shoppers. According to the Times, the shift is a tough one for Arkansas farmers and locals who are used to 50-pound fruits in the traditional oblong shape.
https://www.mnn.com/food/healthy-eating/stories/watermelons-are-getting-smaller