That show has been struggling since day 1 - they would have to commit to a season now and then have to wait months to find out if the film would bolster the series or not. Maybe they decided it wasn't a gamble they were prepared to take.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist