Well they say this is the largest loss "on record." I am sure there have been others, just not on record. They did say 20 foot floats typically floats for three months before sinking, and a 40 footer for about 9 months. So I don't think I would say that is rather quickly. Refrigerated containers are generally inherently buoyant, so they can float for ever.
Every so often this subject pops up... First hand experience with the subject matter..
A legendary offshore danger - Ocean Navigator - March/April 2013
I took these pix about 15 or so years ago coming back on a delivery from the Virgin Islands and about 2 days out from the Chesapeake Bay entrance.