Pumpkins and Watermelons. Why?

I'm endlessly fascinated by turning store-bought food into seed material and then into food again.
I have never bought seed garlic, all of my garlic for planting came either from grocery store or a farmer's market. The results are great by the way.
It's often cheaper that way too. For instance, a packet of Red Kuri squash costs 3.95 at Johnny's while the same squash is $1.50 per pound at the store. I got a small 2-lb fruit so the seeds were cheaper with the squash attached. I may even have a surprise hybrid if I plant those!




_{Figure 1: several hundreds of seeds. There is no way I can plant them all. Maybe I will squeeze in just a couple of plants on top of tulips after they finish blooming}

On Thanksgiving I was cleaning the said squash when I thought about why such fruit exists. I mean, from evolutionary standpoint.

I'm not aware of wild pumpkins but I've heard about wild watermelons; they even grow like weeds in some places. Apparently they thrive in their home Africa. But which evolutionary forces shaped them into their present form? What kind of animal or natural process facilitate seed dispersal?

This Australian website mentions that wild melon's seeds are easily spread by irrigation water. I also noticed that my pumpkin seeds can float. If that is true for all the melons then it makes perfect sense.
Watermelons seem to be adapted to semi-arid areas with heavy rainfalls in spring. The flood waters may pick the seeds from previous year's rotten fruit and re-deposit it along waterways. So these fruit don't need animals for seed dispersal. Humans picked up from there. They used artificial selection to make fruit more "meaty" and sweet to get watermelons and pumpkins as we know them.