Everything doesn't have to have a Comp lock; Spyderco employs the widest variety of locks and designs of any manufacturer.
But for the Military 2, it absolutely should be a Comp Lock, as it is part of a
family of knives - and the other 2 members of the family also employ a Comp Lock + 4 way pocket clip:
Having the M2 share the same lock and clip of the PM2 and PM3 allows users to retain muscle memory and familiarity across model sizes. A PM2 user can easily pick up a PM3 or the upcoming M2 and quickly start opening and closing it one handed with no mental/physical retraining, very handy when you have done a high level of practice with a given system.
Same way a Delica user will have no problem getting up to speed within its family of knives:
Such a 'family of sizes' is famously employed by Glock. The 34, 17, 19, and 26, while different sizes, are otherwise the same pistol, sharing the same exact operating system, trigger, sights, and ergonomics, allowing a user trained with any one model to quickly adapt to the other.
Having the Military 2 use anything other then the Comp Lock would be as absurd as Glock making the 17 model as a DA/SA trigger design, while keeping all the rest of the models as Striker Fired.
Different locks are fine and great, but the M2 is not an appropriate candidate for them.