I agree, I just don't think the series would fit into a single movie
That's what sequels are for 
If they made a whole bunch of sequels, it still wouldn't fit. After all that splicing and plot changing, it still wouldn't work. Say, we condense ten books for each movie giving us a total of about 5-6 movies. Here's what the first one would look like (books 1-10):
Animorphs: The Beginning
5 kids walking home from the mall cut through an abandoned construction site only to find a dying alien who gives them images of the Yeerks and the doom of mankind. Meanwhile Visser 3 shows up, gobbles up Elfangor, the kids then run for their lives. (half an hour to portray this and for character introduction before they all hang out at the mall)
The next day after discovering they can all morph and during the aftershock of this discovery, Jake is concerned about Tom and then Rachel's friend Melissa reveals doubts about her father, leading the Animorphs to doubt and follow Chapman, then find the location of the entrance to the Yeerk Pool, which after getting battle morphs from The Gardens, they try to infiltrate, revealing the horrors within, and Tobias gets permanently trapped in hawk morph. On the other hand they do manage to rescue Ax, who was being held prisoner in the Yeerk Pool (undersea exploration wouldn't fit and would require too much effort). They also discover that Marco's mom is actually Visser 1.
After the failed attempt and barely escaping alive, the Ellimist wants them to reenter the Yeerk Pool to save 2 Hork-Bajir to give Tobias an opportunity to regain his morphing power? Oh yeah, and they get help from Erek the Chee. All while: Jake wants to save his brother, Marco's dad is in depression and Marco is torn that his mom is on the dark side, Cassie is having moral doubts about all this and has slight feelings for Jake, Rachel's parents are divorced and she is using the battles with the Yeerks to release her anger, Tobias is freaking out that he's trapped as a hawk, oh yeah and Ax explodes on Cinnabons.
You get the point.
That's gonna be one crappy 4 hour long movie. All while excluding a whole bunch of awesome plotlines from the books. I'd like to see some other attempts at this too.
The superhero movies are great because there's only one character who they have to develop, whereas the Animorphs are 6. Each character has his/her own story and even with a condensed/changed plot, it's going to be hard to fit into a movie because there's just too much stuff going on.
It would only work if they made a TV series like Heroes, and if the series were to be successful, they could conclude it with an action packed movie. I'd love to see the Animorphs on big screen as much as anyone but it's just not happening.