Just like evolution has a consilience of multiple lines of evidence for it, there is a consilience of multiple lines of evidence against eyewitness authorship of the gospels.
Specifically;
One - the synoptic gospels are called synoptic for a reason - Matthew and Luke are known to have copied Mark, based on evidence such as editorial fatigue. Why would an eyewitness need to copy virtually verbatim, another gospel?
Keep in mind that Mark itself does not record the Risen Jesus and the Resurrection. If Luke and Matthew copied Mark, and made errors due to editorial fatigue, how trustworthy are they?
Secondly - when were the gospels written?
Numismatic evidence is strong evidence that the gospels were written after 70AD, and the “give to Caesar what is Caesar’s” is anachronistic - the coin of Jesus’ day was the Tyrian shekel, and taxes were paid in goods, not coin. Taxation in coinage was implemented after 70AD. (Fabian Udoh, Tribute and Taxes in Early Roman Palestine, p235).
For example, a coin hoard discovered at Isfiya, which contained coins dating from 40 BCE-53 CE, contained 4,400 Tyrian coins compared to only 160 denarii, of which about 30 were of Tiberius.
This makes Matthew, a supposed tax collector, as author of Matthew unlikely.
Thirdly, Geography also makes one doubt the gospel writers knew what they were talking about.
For example, geography made Porphyry doubt the gospels back in the 3rd century; Porphyry knew that the “sea” of Galilee was a tiny lake, not a sea - nobody else called it a sea, and did not take that long to get across - a lake somehow Jesus and the disciples were on for hours and hours.
Fourthly, the current gospels do not match what Christian elders wrote about them in the past;
Papias, a church elder, described the gospel of Mark as a sayings gospel, in no particular order
The Elder also said this, “Mark, being the interpreter of Peter, whatsoever he remembered he wrote accurately, but not however in the order that these things were spoken or done by our Lord. For he neither heard the Lord, nor followed him, but afterwards, as I said, he was with Peter, who did not make a complete [or ordered] account of the Lord’s logia, but constructed his teachings according to chreiai [concise self-contained teachings]. So Mark did nothing wrong in writing down single matters as he remembered them, for he gave special attention to one thing, of not passing by anything he heard, and not falsifying anything in these matters.”[iii]
This is NOT describing our current gospel of Mark, which is not a set of teachings/sayings, and IS in chronological order.
TL;DR - Matthew and Luke copied Mark (thus they are called the Synoptic gospels). Mark is not the original Mark described by Papias. The current gospel of Mark and therefore the other synoptic gospels Luke and Matthew was likely written after 70AD based on numismatic, geographical, and early church documented evidence.