MB stopped producing the nibs in BBB by the mid 1970s. A definitive reason is not known. The nibs that people post that are marked 14C and are two-tone (mostly rhodium with gold on the rim) and 14K and 18K are not BBB unless they are custom made or retipped. Since nibs are not marked, nib with canbe debated as to B vs BB etc., but I have not seen a more modern nib that had a BBB sticker or some other documentation to show it was broader than a BB. I am not talking about 03B with is still available on a 149 as a no cost option.
If you want to spend a lot ofmoney, you can get a much wider nib from the factory through a special order program. They offer music and caligraphy nibs, but you could also order other siezes like BBB or BBBB. I would love a caligraphy nib but I have not saved up to purchase one (probably because I keep buying other pens).
When I read someone has ground one, it's sad.
Ghost Plane, I understand, I also dream of nib BBB.