Because such reasons are contingent. In another cultural context, they would support a different “holy book.”
The truth of revelation must be valid across cultures. The Catholic way provides reasonable, transferable reasons: historical examination → Christ → Church → inspiration/canon. Thus, certainty of faith is not based on the environment, but on Christ’s authorization of the Church.
Sources:
Scripture (EÜ): 1 Pet 3:15; Rom 12:2.
Fathers/Teachers: Justin Martyr (Apologies: Reasonableness of faith).