I think the real issue with the monk is just that most players don't have several archetypes that come to mind when they think 'monk'. Sure, we've seen them use different weapons, and we know at a basic level that some are based on different animals... but they are all pretty much off-shoots of the same exact martial artist archetype.
You say 'Fighter'... and all kinds of archetypes come to mind. The knight, the swashbuckler, the brawler, the solider, the guardsman, the archer, the tactician, etc. etc. Same with the 'Rogue'... the thief, the assassin, the spy, the burglar, the charlatan, the jester, the urchin as so on. Saying you're a Fighter or Rogue does not clue us in to exactly who you are.
But if you say you're a monk? In D&D especially... there's really only ever been one type. The prototypical one. So the need to have official-WotC-designed different 'builds' per se, doesn't seem to be as important in my mind. Now absolutely... the monk can and will probably see individual variations designed by players themselves (if/when the monk is allowed to 'build it yourself' with the maneuver system like the Fighter gets)... but at least in the first Handbook I can certainly see the reasoning for not going overboard with 'martial arts styles'.
But I also wouldn't then be surprised if a book later on did in fact have more monk maneuvers and martial arts styles.