This carefree pluralism is in fact endemic to the Aristotelian tradition at least up to the late Middle Ages, although different thinkers go in different directions on different topics. And again, the reason seems pragmatic: people are not interested in abstract systems simply in themselves -- they are into logic in order to do things with it.
ADDED LATER: AT branemrys.blogspot.kr, pseudonoma adds the following, which I thought worthwhile enough to put here, since (given the current mismatch between my commenting system and Blogger's division-by-country) it would be invisible to most people:
One asterisk I would want to add to your final point, when you write
"And again, the reason seems pragmatic: people are not interested in abstract systems simply in themselves -- they are into logic in order to do things with it."
It seems to me important --if one is to achieve a fundamental clarity concerning this fine point --to stress not only the practical or propadeutic character of Aristotelian logic, but also to its origin in the Metaphysics. Aristotle is not treating of anything like "a priori formal laws" whose intrinsic systematicity is , e.g., a necessary consequence of their source in the unity of transcendental apperception. One *may* not need the Metaphysics to be convinced of the truth of Aristotle's formal logic, but he can in no wise discover this logic himself without making metaphysical assumptions (or overtly engaging in metaphysics, god forbid!). The categories are predicables second and ways of saying being first, and the principle of non-contradiction is, as Book Gamma reminds us, a metaphysical principle before it is a logical one.