Shakespeare wrote more than one good story.
The Bible is a collection of enduring stories, written by 40 writers at a minimum. One question I've never seen a skeptic able to answer:
Please describe why these writers kept piling on fake books for 1,500 years--40 different writers and teams of writers!
Oh no, you are way off base. There are probably hundreds of writers who wrote these books and many like them. We know of many dozens that were not included. There have been a half dozen written in just the last century. They haven't all been included because someone, somewhere decided they were apocryphal.
But your question is an easy one to answer simply by rephrasing the question. Why would a person think adding their voice to a book known throughout the known world (or at the very least their own country) as the truth? Why would someone want to be immortalized like that? Why would they want to promote themselves and their beliefs to others? Why would they want to inspire others to follow them? Why would they want to push a shift in doctrine away from what was a jew only biased religion to one that could be open to the wealthy romans who controlled everything?
I wonder... it's almost like they wanted their religion to appeal to the rest of the world. To have as large a population as possible. It's almost like they wanted to influence world leaders and current events.
After all, what happened not long after the gospels were written? A long line of popes managed to create the wealthiest church in the world. A religion that influenced kings and drove the wealthiest countries in Europe to their knees, A religion who essentially decided which of those writings were included in the bible...
I would say all you need do is look at the impact these authors had on the world to understand their motives.