Because all that pipeline building is so much more expensive than massive troop concentrations in the area and the occasional war.
Pipelines also tend to fuck up your image real bad.
We could not ship oil from an Israeli or Turkish harbour, oh no.
God forbid that Israelis and Arabs developed common interests, who knows what would happen next, peace in the ME?
Let us stop being constructive, we all know that the profits of oil companies must be refreshed from time to time with the blood of patriots and tyrants.