I think its awesome that the books are being rereleased, but I cannot figure out why there is so much time between the books. Its not like they haven't been written already.
A lot of it has to do with the fact that they are also relaunching these to get
new fans. And Animorphs, as we all know, has lot of continuity. So the last thing Scholastic wants to do is to loose an entirely new generation of fans by releasing these books
too quickly. They're going to want to make sure that there is enough hype about these new books-- that there are kids reading them; kids who will be wanting to come back as return customers/fans for future re-releases. It's really all about trying to make a nice big chunk of $$$ out of a property that they know will sell.
(BTW, I'm not intending to put this in completely a negative, big evil corporation kinda-way. There
is genuine fan support over at Scholastic from people that are relaunching this series. And as a fan, it's just amazing to get a chance to relive the entire series all over again. But at the same time, it's also a business for Scholastic. So I'm just being realistic.)