I'm working from memory here, so I may be wrong.
As I recall it, the ME was introduced to great fanfare as a response to the success of the Olympus OM line. The MX followed the ME because of a small but relatively vocal group of customers and potential customers who wanted a manual exposure only model. The MX never sold in the numbers that the ME and ME Super achieved, but was always a useful alternative for a retailer to have on their shelves.
I would expect that there were many, many more people who bought an ME for snapshots and vacation pictures - and that it is the cameras acquired by those people who stock the relatively abundant sources of used cameras available today.