I think the issue here has to do just with overwriting existing data.  There's four things you might want to do to your storage (whether disk, tape, or SSD): 
A) initialize it, B) read from some area; C) Write data to a previously unused area, and D) write data to a previously used area.  Bubble memory can't treat C and D equivalently.  With bubble memory you can't change a one into a zero like you can change a zero to a one  the former requires special processing, the latter does not  and that special processing is several times more time consuming than B or C.  It's such an exceptionally slow process with high overhead, that your perception of your SSD would probably be unfavorable if the manufacturer allowed you to perform it on small chunks of data.  An analogy  if you're going to drive a long way to the store, get everything in one trip  even if you don't need it immediately  because if you have to make two (or three or four) trips you won't be pleased with the result.