Once again, Ford already DID sell that here, except for the diesel part. You can argue all day whether the Sport Trac is/was a 4 door Ranger or not, but the fact is, it was a 4 door, it had the exact same size bed as the foreign 4 door Ranger, same payload as a Ranger, and same drivetrain. If they had different sheet metal Ford could've easily called it a Ranger.
They didn't sell that well. If they did, Ford would still be making them. So, next time you wonder "why don't they sell those here?" Well, there's your answer.