It was a move by Cedar Fair, not B&M.
The point of a safe restraint system is to have redundancies in the design, so if one design should fail the next will work. That being said, the B&M clamshell design is already a redundant system, with a flawless track record to my knowledge (anyone else know of a B&m clamshell incident?). Adding an additional seat belt certainly makes the system safer, but the purpose of adding the seat belt certainly was not the result of an incident with the B&M restraints.
Rather, the timing of the B&M hyper seatbelts follows the Texas Giant accident last year, which occurred on a Gerstlauer train that was only a lap bar restraint (no seatbelts). If I were a gambling man, I would venture a guess that Cedar Fair's addition of seat belts could have been cause by the separate Texas Giant incident. Partially precautionary, partially for the sake of Cedar Fair's lawyers, and partially a rhetorical move to show that the rides are safe.
All that being said, these seat belts are not necessarily permanent. Cedar Fair has a track record of adding and subtracting seat belts to rides - for instance, while they added seat belts to a number of Arrow loopers, they removed seatbelts from Arrow Swinging trains.
So the seatbelts are dumb, no one honestly knows why they were added, they slow down capacity, and we can hope Cedar Fair removes them in the future.
