I had a friend who was high up in a refinery years ago, and he once explained to me that many parts of the refining process are held separate as an artifact of rail companies and old oil kings being close knit.

I guess the idea was if you make it so we have to carry your product back and forth, we'll only use your product on our trains. The concept carried over with pipelines, people with interests in both industries ensured that the IP and patents needed for mass consumption were protected to essentially create the need for pipeline infrastructure. Otherwise they would have just bought miles of land and shipped near complete product to shore instead of the current back-and-forth.

I'm paraphrasing info i heard 20+ years ago, but the general take away is: oil production is siloed so the rich could get richer.