FWIW I’ve read all the early Fathers.
Their quotes from New Testament Scripture are frequent (and there is much scholarly discussion, based on what they do or don’t quote or paraphrase, about what was available to each). But in general their quotes are just that - recycling of words that clearly carry traditional or apostolic authority. They seldom give references, or at most something vague like, “as the apostle says…” or “the Laord taught…” And of course the actual lists of canonical books are much later, elicited by particular needs.
So it is scarcely surprising if the gospel authors are not specifically attributed - they are simple used by the early writers. Just as now a Christian might say “It is more blessed to give than to receive” without even knowing the reference, or even that it’s one of the few NT sayings of Jesus not in the canonical gospels (but quoted by Paul).
It’s just as in a science-faith blog, where the phrase “creationism in a cheap tuxedo” is understood by all without needing attribution, to the extent that in a blog on atheist use of theology I could parody it as “Richard Dawkins in a cheap cassock” knowing that my readers would get it.
By today’s standards not naming a source is lazy scholarship - but in a non-literary culture it’s a sign of authoritative texts that are familiar enough to both author and reader to be common currency. The question then becomes how those gospels became universally authoritative so early, in a church scattered across the Roman Empire.
Someone like Ignatius before 107 could shoot off letters to local churches in several nations on his way to execution in Rome, knowing that his many direct and loose quotations and allusions from 3 of the gospels and 12 other NT books (from memory, certainly) would be familiar to Christians wherever he went, and would bolster his arguments.
Their authorship and provenance would clearly have had some relevance to that, as would the sources those authors used. When they did later come to be attributed, either in mss titles or in literature, to Matthew, Mark, Luke and John, they were universally recognised by those names. This suggests that the four authors were universally known in the churches.
That said, Eusebius quotes Papias (early 2nd century) in naming Matthew and Luke’s gospels. Justin Martyr in the mid 2nd century uses all four gospels without naming them, but appears to link Mark with Peter (which accords with tradition about Mark’s main source). By the later 2nd century Irenaeus is stressing the very fact of four gospels as being as foundational as the cardinal points of the compass.
I assume that someone on this long thread has already pointed out that, if the authors were a late invention, they’d be an odd choice: neither Mark or Luke were apostles and are minor figures - Luke was not even a witness to the ministry of Jesus.