Yeah, I think it's related to the problem of "Concrete Meaning" (as discussed at length in
http://www.enworld.org/forum/showth...ses-Have-Concrete-Meaning-In-Your-Game/page65). Fighters and their subclasses have little "Concrete Meaning," in contrast to many 5e classes. To a certain degree, I'm sure this was intentional - people expect the fighter to be a flexible class, to represent many different character types, and the 5e fighter delivers on that, at the expense of being "generic."
I like the idea of subclasses with more concrete meaning, I just don't want them to be BM knock-offs.
Here's the thing... I think these kit re-dos are their attempt to actually GET at "Concrete Meaning". And they're using the Battlemaster because it is what I think
they think is the "real" Fighter class. The class they would point to as being the baseline Fighter, because that's the one that has their mechanical martial creation-- the Superiority die. The Champion exists because they felt the need to have a "simple" Fighter, but it's not the one they look as being equivalent to the Cleric or the Wizard. I think the Battlemaster is what their default Fighter class
would be if they didn't provide the simple one too.
So if we say for the sake of argument that Battlemaster = Fighter in their eyes... we now look to the
subclasses of that "Fighter class" to get at the specialties that include all the story and fluff. This is where we'd find the Samurai. The Gladiator. The Scout. The Cavalier. All the fluffy sub-classes the Fighter gets that the Cleric gets with their god domains and the Wizard gets with their schools of magic.
Can you theoretically make Cavaliers, Scouts, Gladiators, Samurai, Myrmidons, and the like just by using the Battlemaster as-is? Sure. But why aren't people doing that? In the thread you mentioned, it was brought up that you could make a book of "Fluffy Fighters" just by making specific builds of the Battlemaster and layer on some story as to why you selected this maneuver or that maneuver. But it didn't seem to gain much traction. I would suspect though that by doing
this... not only selecting this maneuver and that maneuver but also getting EXTRA bits you can't ordinarily get from your baseline Battlemaster... is the way to inspire people to play them, as well as make a reason for WotC to possibly publish them in a book. Because there's extra mechanics for each sub-class, so you aren't just printing a book of "ideas", which would probably irritate people.
For my money... if "spells" are the baseline mechanic for all spellcasters and which can be distributed across almost every single class in the game in some form or fashion... then "superiority dice" can form the same function across several different martial classes too. I don't see why every martial classes needs to have their own individual martial mechanic without any overlap whatsoever (like we currently have in Rage, Superiority Dice, Inspiration Dice, Sneak Attack, Smite, Flurry of Blows and Hunter's Mark). More than one martial class could share a mechanic. Or at the very least... the one "sub"class that has it could share it amongst other sub-sbclasses.