People drive transit vans and they ride in them, but they don't spend a lot of time thinking about how transit vans came about. They actually appeared out of necessity, though, because there was an increasing demand for something that could carry a few people and their gear without being as large as a bus and with a decent ride. Ford created the first popular transit van in 1965. There were creations before then that were essentially bulky boxes on wheels, but they were so uncomfortable that no one liked to use them very much. It was much better to have something that people could ride in comfortably but that could still carry a lot of gear and equipment quite easily. Ford saw that there was a need, so it cornered the market on transit vans, and it still has that market, as there aren't any serious competitors.
The van started evolving almost as soon as it was created. The grill was changed in the early 70s to make the van look more like a car. It was still pretty boxy, but it had a little bit more style that way. Style and comfort additions were the most common ones that were seen with the van all the way throughout history. It ran good and did what it was supposed to do from the start, so the issue became how it could be made more comfortable for the people who would drive it and ride in it. Things like seatbelts and other safety restraints were installed as mandated, but the overall design was mostly left up to Ford - and the company took its responsibility very seriously. If people didn't like the transit van it wouldn't get purchased and used, and Ford would lose money.
Naturally that's a very bad thing to happen, even to a large company that can probably afford the loss, so the fact that Ford held its own and kept the transit van popular is a testament to how serious the company was about taking care of its customers. Transit vans are seen on the roads today more frequently than they used to be, mostly thanks to the innovations that Ford worked so tirelessly on. There are other kinds of transit vans out there, but Ford remains the most popular and other companies mostly follow the same design and style in an effort to compete with the market leader.