To your last point, the reason was that the Olympic was dealing with some manufacturing issues and couldn’t be insured unless it was basically rebuilt for a new inspection.
Instead of rebuilding it, they secretly renamed it the Titanic so it could be insured fraudulently under the Titanic’s insurance, then intentionally sank it to claim the insurance on it. Now they have a good ship (the real Titanic) which will pass inspection as the Olympic, and they have the insurance payout from the sunken Olympic which shouldn’t have been able to be insured.