Why do atheists even bother about debating Jesus?

[Confused Ape]

Have just looked up Justin Martyr (AD 100–ca.165)

Some time afterwards, he chanced upon an old man, possibly a Palestinian or Syrian Christian,[8] in the vicinity of the seashore, who engaged him in a dialogue about God, and spoke of the testimony of the prophets as more reliable than the reasoning of philosophers. It was this argument which, Justin avers, kindled in him a love of Christ, and led him to embrace the Christian faith.[9] He was influenced in this by the fearless conduct of the Christians facing execution (Apol. 2:12).

This was a time when various Gnostic sects were around. Gnosticism

Gnosticism (from gnostikos, "learned", from Greek: γνῶσις gnōsis, knowledge; Arabic: الغنوصية‎) is the thought and practice, especially of various sects of late pre-Christian and early Christian centuries, distinguished by the conviction that matter is evil and that emancipation comes through gnosis (knowledge).

Although some scholars still postulate pre-Christian gnosticism, no evidence has been found to date. It is now generally accepted that gnosticism developed into a coherent movement only in the second century CE.[3][4]

There were various Non-canonical gospels which didn't make it into the Bible.

In addition to the four canonical gospels, early Christians wrote other gospels that were not accepted into the canon, some of which are discussed below.

It's possible, then that Justin-Martyr could have been a Christian without ever hearing of Paul or the canonical gospels because there were a number of different Christian sects around at the time.

There is a bit of evidence that Pontius Pilate actually existed because of the Pilate Stone.

The Pilate Stone is the name given to a block (82 cm x 65 cm) of limestone with a carved inscription attributed to Pontius Pilate, a prefect of the Roman-controlled province of Judaea from 26–36. The stone is significant because it is the only universally accepted archaeological find with an inscription mentioning the name "Pontius Pilatus" to date.[2][3]
It is likely that Pontius Pilate made his base at Caesarea Maritima where the stone was discovered, and occasionally went to Jerusalem when needed.[4]
The Pilate Stone is currently located at the Israel Museum in Jerusalem.[5][6]

Pure speculation here. Jesus kept telling people to stop believing what the Pharisees said so he annoyed the establishment. The Pharisees did a deal with Pilate to get rid of him and Pilate agreed in order to keep the peace. Nobody bothered to write about it at the time because the only people who really cared were the Pharisees and a handful of followers who were Jesus's close companions. If he'd come back from the dead it would have caused a sensation across the Roman Empire so I think we can safely assume that the resurrection story got added on later.