The church did not choose the books of the cannon, they discovered what God intended to be in the New Testament
The canon is a list of authoritative books more than an authoritative list of books
The early chruch fathers can help answer which books because they were closer to the events than we are
They recongnized the inspired books very easily, the early church fathers were disciples of those who wrote it.
For example: John > Polycarp > Irenaeus
While there was no question from of the early church fathers what was inspired, most the New Testament was accepted by 200AD, making it offical by the Council of Hippo in 393AD
See list of early church writting referencing books of the New Testament pp369
Why not eariler? Because during the first few centuries, Christianity was generally illegal until about 313AD