Yup as has been said, the files are to big.
I have sent the lore book and almanac to Amazon and had it converted, only for it to break everything and look horrible with large gaps, blank pages and everything. the Strat guide is just way to big to be sent via email, and even if it was sendable you'd still have the same issues as with the lore books.
having a .mobi/.epub version would be the best solution.
Also you can't convert the strat guide in calibre (i tried multiple times, including on a 12 core system), my guess it's ust to big for calibre to work with. But again you'd just get the same issues as with Amazon