An interesting question was posted on the SCWF.
Why is the Landmaster 10th Anniversary not more popular?
I think it’s not more popular because it’s not a diver.
First, there is a regular version of the LM (SBDX007) that competes with the 10th anniversary edition for sales and together, they compete with the MM. I could be wrong but I see the MM as a competing product to the LM because they have the same 8L35 movement and have similar one-piece case of similar size and thickness. They are only competiting within the Seiko family.
Price wise, they are selling at similar price point and it becomes a question of which field or style do you prefer. Most of us would choose the MM over the LM as dive watches generally tend to be more popular.
Of those who have both, most of us probably bought the MM first, like myself.
Picture courtesy of Jayhawk’s Watch DB