The op was about the MP volume not Leica total volume.
Leica acknowledged that the MP was a model that they did to keep (sic diehard) people happy, they based it on extant production items the M7 (e.g. the MP uses the M7 chassis, and did it to high standards of finish and top plate text... They did not expect it to sell in any real volume so priced it as a lower volume flagship.
They were surprised when it then outsold the M7 at least initially, but the customer is always right so they have kept on making them, and the custom accessories like the faster rewinder...
Which last is also a useful option if you have a M2 or M3... If you have a M6 already Id stick with it, rather then upgrade, they both have the same sensor pixel count and ISO after all