[Prudence]

It's not like the Catholic Church has helped its cause any. Frankly, many people don't have a clue about the first couple centuries of Christianity, think the New Testament gospels were written contemporaneously with Christ's life, and (particularly Protestants) are shocked to learn about apocryphal texts. (This is likely an exceptional audience.) Based on my experience with people I know, this can translate as a sense that information has deliberately been hidden from them, rather than their own failure to investigate. And gosh, if the Church is "hiding" the gospel according to Thomas, why, they might be hiding anything!

There's just enough not-actually-known, plus some not-widely-known, and maybe a pinch of deliberately-kept-unknown, that conspiracy seems, if not probable, at least possible.

Heck, even I sometimes indulge in a few "what aren't they telling me?" fantasies. That's what makes historical fiction fun.

However, the Catholic Church doesn't exactly have a reputation for transparency right now, so I can see where they'd worry that this would increase mistrust and skepticism.