It's because we can read Scripture, study history and think.
The Apostles were missionaries. The Apostles did not serve as bishops, except James the brother of Jesus in Jerusalem. Decision making and organizational structure of the early church was congregational. The idea of a direct line is a myth as there are gaps in it, the most glaring being the Apostles not directly appointing the next generation of leadership. The monobishophoric system did not emerge until after the Apostolic era and was not created by the Apostles.
In addition the merger of the church to the state and the systematic creation of doctrine that separates the believer from God the Father, God the Son and the Holy Spirit leads any Bible believing Christian to reject their claimed authority.
The breathless ease with which the enemies of the Church ignore the scripture they profess to follow is amazing.
3 Wherefore, brethren, look ye out among you seven men of good reputation, full of the Holy Ghost and wisdom, whom we may appoint over this business. 4 But we will give ourselves continually to prayer, and to the ministry of the word. 5 And the saying was liked by all the multitude. And they chose Stephen, a man full of faith, and of the Holy Ghost, and Philip, and Prochorus, and Nicanor, and Timon, and Parmenas, and Nicolas, a proselyte of Antioch. 6 These they set before the apostles; and they praying, imposed hands upon them. 7 And the word of the Lord increased; and the number of the disciples was multiplied in Jerusalem exceedingly: a great multitude also of the priests obeyed the faith.(Acts 6)