How do you know? Who were Matthew, Mark, Luke and John?
I’m going to jump in (an out!), but it seems to me that the folks Jesus was getting his message to were the ordinary folks. Not sure how literate they were back then. And I heard an interesting conjecture on why the scriptures weren’t written for another 20 to 30(???) years or later after Jesus. The thinking goes that the disiples thought Jesus would return in their lifetime. But after awhile they realized that might not be so - and so got to writing Jesus’ stories down.
Sort of like my mom writing her “memoirs” and talking about the roaring 20’s, the Depression, WWII, etc. She got to writing down her memories about 20 years ago when my dad was sick and the feeling that she better get some stuff down in writing to be able to pass it on. (And she still keeps adding to them when she thinks of something!)
Of course many of the stories I heard or witnessed as a child. If she had made up some wild stories my older kids and I would have called her on them.
And while there are lots of arguments on the veracity of the Bible, etc. - it does come down to faith. However, many of the best Christian apologetics around set out to prove the Bible wrong. And based on the evidence - gained faith.