Yes; because the Catholic Church gave them her stamp of approval and orthodoxy.
The first alleged infallible ruling on the canon, by Catholic standards, occurred in the sixteenth century at the Council of Trent. Did nobody have good reason to accept the Biblical documents earlier? See my article here, in which I document the fact that ancient Christians referred to their confidence in the Divine inspiration of Biblical documents long before the Council of Trent, often for the same sort of evidential reasons I've cited in support of those documents. See here regarding the ancient use of the canonical criterion of apostolicity, which doesn't require a "stamp of approval" from Dave's denomination.
In another article, in response to my comment that Eusebius' rejection of 2 Peter doesn't represent a rejection of the book by a majority of Christians, Dave wrote:
Jason the amateur historian says this. But F. F. Bruce, the credentialed Protestant Bible scholar, cites Eusebius about 2 Peter and appears to differ:
We may think, for example, of the widespread hesitation in accepting 2 Peter .[Cf. Eusebius, Hist. Eccl. 3. 3. 1: "But the so-called second epistle [of Peter] we have not received as canonical . . ." ]
(The Canon of Scripture, Downers Grove, Illinois, InterVarsity Press, 1988, 263)
There was considerable hesitation about 2 Peter, but by the time of Athanasius it was no longer a disputed book in the Alexandrian church or in western Christendom.
The most disputed of all the disputed books of the New Testament is probably 2 Peter . . .
Origen is the earliest Christian writer to mention 2 Peter; it does not appear to have been known much before his day. [footnote: Eusebius, Hist. Eccl. 6. 25. 8]
The only comment Dave has cited from Bruce that seems specific enough to qualify as a disagreement with my position is the last passage he cites. But none of the evidence Bruce mentions leads to his conclusion. Bruce cites what Origen said about the disputed nature of 2 Peter. But, as I've argued elsewhere, Origen himself accepted 2 Peter as scripture, and the passage Bruce cites in Eusebius doesn't specify how widespread the doubts about the book were. Given how widely accepted 2 Peter was in the fourth century, a majority acceptance of the book earlier makes more sense of its later status. I'm not aware of any obstacle to that conclusion in the evidence we have from the earlier sources. Eusebius classifies 2 Peter as one of the books that's disputed, but "known to most ecclesiastical writers" (Church History, 3:25:6), and he's including earlier generations in his analysis. He's not just referring to his own generation.
Thomas Schreiner writes:
"Origen noted that some doubted the authenticity of 2 Peter (Eusebius, Hist. eccl. 6.25.11), but in his own writings he cited it six times, and we can conclude from this that the doubts of others were not compelling to him. It is also likely that Irenaeus knew and used 2 Peter...The evidence is disputed, but it seems likely that Clement of Alexandria wrote a commentary on 2 Peter (Hist. eccl. 6.14.1). Such a commentary would indicate a high estimation of the letter and would cast doubt on a late forgery since it is unlikely that Clement would have no information about its pseudonymity if the letter were written in the second century....It is also quite likely that Apocalypse of Peter was dependent upon 2 Peter. If so, 2 Peter was in circulation in the early part of the second century." (1, 2 Peter, Jude: The New American Commentary [Nashville, Tennessee: Broadman & Holman, 2003], p. 263)
Schreiner also cites other sources and goes into much more detail. 2 Peter does seem to have been widely known before the time of Origen. F.F. Bruce's conclusion is dubious. Dave hasn't given us any reason to agree with him.