Why isn't much Information about Leonardo da Vinci's Family Tree?

I've been looking for information about Leonardo da Vinci's family background through the internet. But For some reason many sites say that not much is know about his family background. His family only dates as far as his great grandfather, and regarding genealogy thats not alot. You figure that this time near the Renaissance, they keep better records for their family members. Especially regarding one of the most famous historical figures from the Renaissance period. Is this really the case, that not much was recorded about his family history. Or am I not looking hard enough? Is there a book I can check out that can tell me farther about his family history, or am I going to get the same thing I'll get from the internet? Please help.