[cmsmith]

I'll take a guess:

300 feet is awfully deep. If you believe that 300 feet of draft is needed to get the stability they need, then this seems like the only way to get it. There are no ports, or even semi-protected waters, where you could build, launch, or dock something like that without it running aground.

Some quick research shows that the deepest draft on oil platforms is in the range of 25m (1/4 of the FLIP ship), and further that this ship was built a decade before the development of floating oil platforms.