Yeah, this was the author's response to fans being upset it didn't end cleanly (with a bonus wrestling reference)
Also, spoilers for a 20 year old YA adult novel series.
"Animorphs was always a war story. Wars dont end happily. Not ever. Often relationships that were central during war, dissolve during peace. Some people who were brave and fearless in war are unable to handle peace, feel disconnected and confused. Other times people in war make the move to peace very easily. Always people die in wars. And always people are left shattered by the loss of loved ones.
Thats what happens, so thats what I wrote. Jake and Cassie were in love during the war, and end up going their seperate ways afterward. Jake, who was so brave and capable during the war is adrift during the peace. Marco and Ax, on the other hand, move easily past the war and even manage to use their experience to good effect. Rachel dies, and Tobias will never get over it. That doesnt by any means cover everything that happens in a war, but its a start.
Heres what doesnt happen in war: there are no wondrous, climactic battles that leave the good guys standing tall and the bad guys lying in the dirt. Life isnt a World Wrestling Federation Smackdown. Even the people who win a war, who survive and come out the other side with the conviction that they have done something brave and necessary, dont do a lot of celebrating. Theres very little chanting of were number one among people whove personally experienced war."