that is because they thought they were being renewed so the "ending"wastacked on.
Nathan since the blue butterfly episode has been enamored with being a P.I. on a show.
he did not want beckett and castle to become a couple, or get married.
most of the FANS who fell in love with the story of them, wanted them together- the ratings proved it, the highest ratings were seasons 4-6 with 5 and 6 - with them being together as a couple/engaged being the highest, the fiasco of the finale of season 6 and the idiocy of his disappearance(rumors of that story line being driven BY nathan) and no wedding the fans wanted = ratings go down by about 20% over and above the drop in live viewing. then comes the idiotic locksat story line, which drives them apart- AGAIN (again pissing off the "caskett fans" even more fans stop watching the show. season 8 was by FAR the lowest rated season of the show- it -again rumors only- was due to nathan not wanting to share screentime with stana = HE was the "star" of the show, HE was the titular character- it should be "his show".
screentime for the two of them plummeted since season 6, them being- on screen in the same scene (one camera show with both faces seen) went from about 25 minutes an episode,,,to under 8 minutes an episode.
fans of the show noticed. and did not like it, the number 1 call for - besides improving the writing on the show was...more onscreen time- together- for nathan and stana,...
everything pointed to being renewed -most if not all "renewal" scorecards had Castle as a safe bet or a sure thing by the beginning of april, when news was announced that Nathan had signed a new contract with ABC Studios, (both nathan and stana signed 1 year contracts last year) then the news leaked that Stana and Tamala were not coming back next year (let go for budgetary reasons is the official ABC line-when beckett's char - in my opinion- was one half of the heart and soul of the show.(nathan and stana-together)
with the rumors of nathan having in his Contract -last year- that he will not work with stana for more than 2 days an episode, and that in one of the conditions for The new contract was that Stana would be Gone. The fanbase erupted in anger about it.
also the co-lead for the show was let go for "budgetary reasons" while secondary characters stayed on- ryan, espo, alexis, martha, haley & lanie are all secondary characters that could be "let go" without a major retooling of the show, BECKETT being gone required an entire REDO of the ENTIRE show premise.
note: season nine would have been focused on Castle being a P.I. and most of the cases of the week would have been about that -him alexis and toks -ryan and espo
prior to the news most of the fanbase wanted castle renewed for season 9(60-70%).
AFTER the news almost every Poll about renewal had it 90+%-essentially- cancel the show, or renew but only if stana(beckett) was back.
with them already announcing - no stana- and the ramifications of ratings being - probably- less than Half of what they were This season, ABC decided to cancel the show- AFTER- the last episode had been filmed.