The popularity of 'the goonies fanfiction' comes from the love for the original movie. Fans are so attached to the characters that they want to see more of their adventures.
It might be that Sonic is drawn to the Goonies because of a strange energy or object that they've found. Since Sonic is often involved in protecting powerful items, he senses this and comes to check it out. The Goonies could initially be a bit wary of him, but as they see Sonic's good intentions, they team up. Together, they use Sonic's abilities and the Goonies' knowledge of their area to solve whatever mystery is surrounding the object or energy.
The 'Goonies Novel' is likely about the adventures of a group of kids, probably filled with mystery, treasure hunting and friendship. Just like the movie, it might tell the story of the Goonies as they face various challenges and try to achieve a certain goal.
Definitely not. The Goonies is a fictional tale. It was crafted to give viewers a thrilling and fun experience, not based on any real events or people.