It's not that they are unable to entirely, it's that they are unable to economically. If you're paying more to refine your oil than what it costs to sell/use it, you're taking money away from your industries that depend on oil. Eventually the businesses would go bankrupt. Since we have a "free market", the market doesn't want to lose money, so it will run at a shortage with high prices, or stop running entirely (whole refineries can shutter due to losses). We saw this in practice during the 70s when OPEC forced a shortage. We are still vulnerable to the same thing.

The same shortages seen in the 70's would have already happened this year due to the Straight of Hormuz - except China saved the whole world from shortages by cutting its own imports of oil by 50%. Their massive drawdown created a buffer in the world oil market that everyone else pulled from. This is why China's oil reserve and non-OPEC imports make them the most powerful country in the world now. They effectively exist in a separate oil system with plenty of capacity for themselves, while we remain reliant on OPEC.