Why was there so much diversity in ancient baptismal beliefs and practices?

Gavin Ortlund just posted a video about how the historical evidence favors credobaptism over paedobaptism. I agree with him, and I've written about the subject in other posts, like here.

What I want to focus on in this post is why we see so many differences, and often contradictions, among the ancient sources on baptismal issues if what critics of Protestantism tell us about the nature of the church and other relevant issues is true. If there was one church that all or a large percentage of these sources belonged to, with the sort of unity people like Romans Catholics and Eastern Orthodox often claim they had in the past, with their infallible church maintaining all apostolic teaching in every generation, providing guidance, scripture interpretation, the settling of controversies, and such in the way modern Catholics and modern Orthodox often claim their church provides, why do we see such diversity in the historical record on baptismal issues? Some of the differences went on for centuries, sometimes a millennium or more.

Hermas (who lived in Rome, a significant context in relation to Roman Catholicism) advocated postmortem baptism (The Shepherd Of Hermas, Book 3, Similitudes, 9:16; see, for further discussion, Anthony Lusvardi, Baptism Of Desire And Christian Salvation [Washington, D.C.: The Catholic University Of America Press, 2024], 15-18). As I discussed in a recent post, people like Cyprian thought John 3:5 refers to two sacraments, not just baptism. Cyprian, along with others, also disagreed with Roman Catholicism about the validity of heretical baptism. As I discussed in another recent post, the concept of baptism of desire was widely absent or contradicted early on and didn't become a majority view until well into church history. And there are many other baptismal views the early sources held that are wrong by the standards of modern Roman Catholicism and modern Eastern Orthodoxy. For a discussion of a lot of other examples, see here. The views we find in the early sources include credobaptism and justification apart from baptism.