Look who is busy with new threads yet again...
Don't forget, you can still use Swift/Immediate actions, not only meaning with a Belt of Battle you can recover once per day as a Swift action but also use a Boost or Counter. Not to mention the tons of other combos presented (perpetual incorporeality).
Maneuver usage has a very steep curve to it. IE look at Diamond its self, of your 8th level choices only one is a strike (x4 damage), after that you only option is 7th level for an attack till you miss Strike that imposes a cumulative -4 penalty (and you're not even a full BABer), odds are you'd be lucky to hit a second time, good luck with that fourth to be comparable. It comes to the number of Maneuver schools known is the number of effective rounds you'll have, after that your combat ability drops significantly.
And it's not just Strikes either, you'll be burning Boosts/Counters at a fairly rapid rate if you know what your doing, three Combat rounds is 6 Maneuvers spent, you don't exactly have an infinite number of 'Ready's. You'll need to refresh soon or you'll be behind that of a normal mundane. Remember, you don't have the Rogue's SA to offset your pitiful damage, or the Fighters godaweful Feats. Without Maneuvers you're worse than the lowest of low, the Barbarian.
The last point to consider is you are not the Warblade. You have a significant number of Maneuvers Known, so instead of focusing on the absolute best series you can use you can pick some circumstantial ones and Adaptive Style can pull them in. Like for example Leaping Flame is an excellent counter against range abusing opponents but worthless if they stick close. As part of your refresh you can pull that on in and even Counter with it within the same round.
tldr; four reasons. Good combo potential, more deadly offense if used once every couple of rounds, prevents you from running out in extended battles, lets you Adapt your Style to the current encounter.