It was because Kii was the place where the powers such as temples and kuni ikki (uprising in a province) which opposed the idea of central government topped by tenkabito (person becoming the ruler of the country) had ruled.
紀伊は寺社勢力や国一揆といった、天下人を頂点とする中央集権思想に真っ向から対立する勢力の蟠踞する地だったからである。