Maybe Protestants simply have a higher view of Scripture since it is sufficient and complete revelation for the Protestant.
It may surprise you to learn that Catholics also accept the material sufficiency of scripture…we simply reject the formal sufficiency of scripture which Protestants claim but cannot prove.
Does scripture claim to be sufficient? If so, please provide chapter and verse, please.
I never could understand how the Catholic Church can have a growing ongoing source of revelation in sacred tradition and not consider new sacred tradition being new revelation from above.
Do you believe that revelation ended with the death of the last Apostle? If so, please provide chapter and verse, please.
Despite the fact that this is NOT taught in scripture, it is true, and Catholics agree that the faith has been delivered once for all to the saints. Sacred Tradition is NOT new, but a different mode of transmission of the one gospel.
How can the Magisterium add to the Faith that was once for all delivered to the Saints as revealed in Scripture?
The Church does not ADD to the faith; however, we come to understand that faith more deeply over time. This is development. For example, the early Church did not understand the Trinity or the incarnation as thoroughly as we do today.
It is a self-serving position to make a claim that the Church cannot error, or is protected from error in the areas that is claimed that it cannot error.
It would be self-serving if the Church merely asserted these things about herself; happily, the Lord Jesus Himself promised that the Church would be protected from error.