Why did some delegates at the Constitutional Convention want to keep states rights?
You must remember that back then they had no example of a workable balance between a central government and the provinces. All the governments of the world were monarchies, and had been since the time before Julius Caesar 17 centures before. Their fear of centralized government was well-founded. At the time, the American colonies were almost individual countries that shared a common language and mother country, but little else. The southern colonies were wary of the northern industrial and financial might, the northerners were wary of the slavery and aristocratic pretensions of the southerners. All were wary of the concept of a central government that could assume infinite power and become yet another dictatorship, or in those days, monarchy. The notion of “states rights,” that power would be decentralized, was promulgated in order to keep the otherwise fractious delegates together, and indeed the compromise method we now call the “Federal” government apparently worked.