Rather abruptly, it was announced that Cage of Eden was no longer going to be serialised:
2013's combined 4th/5th issue of Kodansha's Weekly Shōnen Magazine is announcing on Wednesday that Yoshinobu Yamada is ending his Cage of Eden (Eden no Ori) manga series in three more chapters. If Yamada does not take a break, the manga will end in the 8th issue on January 23.
Anime News Network
I can't find a definitive reason as to why the series was finished when it was, but the general consensus on the web seems to be that a drop in sales led to the publishers, Kodansha, halting the production:
"Sadly the manga was cancelled by the publisher and not the fault of the author. He was given at least a month to end his story."
"The series was killed off so the author had to end it within a certain chapter, hence the ridiculous rush ending."
"The ending was terrible because the manga got cancelled and the author had to end the story in a few chapters."
"No, it's not very popular. Last volume that went on sale sold 40K copies which only put it at number 23 in the manga charts it then dropped out of the top 50 the week after."
In any case, the reason for the completely rushed ending is definitely due to the series' cancellation.