I wouldn't say that movie killed the popularity at all, and I doubt if White Wolf's sales would either (if anything, I believe sales on Vampire: the Requiem have likely increased in the
4E announcement era from gamers wanting to invest in something else when 3.5 goes out of active print - another possible factor). I will, however, point the finger at
Moonlight (that recent vampire detective drama from CBS) on adding fuel to the fire of some of these daywalkers (likewise on feeling the need to admit what they are - I've only seen snippets of the show, but in two out of those three attempts at watching it, the main vampire was talking about what he was with a normal human). Every time literature or pop culture gives another example of a way for vampires to ignore their intended weaknesses, someone will think the ideas are good, pick them up, and run with it. Then it'll fade, and things will go back to the way they were.
Like the others have said, it's just the natural cycle of trends and fads, turning back to an old standby, especially with vampires' self-propagating nature. Today it's too many vampires, tomorrow it'll be too many vampire slayers (with far fewer vampires to slay). As always, it'll run its course back into the normal levels before too long.