Well for one, open access requires the Internet. The closest thing to "open access" prior to the Internet was the willingness of universities to allow unaffiliated members of the public to walk into libraries and read the journals stored there. It took the Internet for there to even be something to figure out.
Beyond that, it is just the general time needed for society to adjust to a new way of thinking; people, scientists included, do not start questioning the status quo overnight.
Beyond that, it is just the general time needed for society to adjust to a new way of thinking; people, scientists included, do not start questioning the status quo overnight.