A lot of businesses are impacted by the price of oil even if they don’t directly take delivery. It serves as a really valuable hedge for airlines for example, where it’s a key cost driver, even if it has to go through a refinery first.
Seriously, do people enter into contracts like this in other parts of their life?
As for trading exactly the item you will need delivery on, that may be hard to find. Standardising on a contract that's "close enough" allows crude oil producers to trade with airlines, bus companies to trade with refineries, etc, even if they all care about different products.