Simply because Praba never wanted anything other than the Ealam in the first place...
Rmember that the talks started in the post-period of 2001 9/11..in that time... TERRORISTS were the number one hate word around the world... so it was also a very bad time for the LTTE to collect money & promote their stuff... It was a time for them to lay low & Hibernate until the storm passed over....
Along came Ranil with the peace talks offer.

...just what the LTTE needed so they promptly signed it in 2002...
bt LTTE kept on recruiting, kept on stock piling wepons, kept on aquireing more land & the Army couldn't do anything about it because they were ordered not to do so... Ranil played right in to the hands of Prabakaran...
so after a couple of years, after praba getting everything he wanted & Ranil giving away everything except hi ass in order to hav his peace at any cost, the Terrorist hunting mania slowly went away... people slowly forgot about 9/11 & time for Praba to be active again to re-strat the fight against eelam
Then in the election paraba kicked out Ranil gloriously.. Ranil unknowingly helped the LTTE to lay low in the hunting season & prepare for the incoming Ealam war grandly & with more freedom than they ever had before..so Ranil finally went away crying after doing his duty...
LTTE's primary objective is eelam.. they never gave that up..Ranil was taken for a grand ride & then dumped..
thats why I always thought Ranil got fucked Royaly..