It's a question of ultimate doctrinal authority in the Church. With Scripture and Tradition as interpreted by the Magisterium in the Catholic Church, what is orthodoxy is a little clearer, despite individual clerics and laypersons going off the rails. While sola scriptura of Protestantism does provide some clarity, it is much harder with private judgement in the interpretation of scriptures to define what is Protestant orthodoxy in any particular denomination. And of course your K. Jefferts-Schorri, V. G. Robinson brand of Protestants don't even accept Scriptures as a standard.
Protestantism isn't monolithic. My church adheres to a written confession which doesn't change.