Louis is a troubled vampire whose humanity didn't die when his body went through its "mortal death". He wanted to tell his life story, which the interview is.
Had he wanted blood, he would have gotten it in a manner much easier than luring the interviewer for the whole night.
These are his comments from the book, right after the boy (the interviewer) asks to be turned into a vampire:
"This is what you want?", he whispered, his pale lips manifesting only the barest trace of movement. "This... after all I've told you... is what you ask for?"
He also adds:
He looked again at the boy. "I've failed", he sighed, smiling still. "I have completely failed."
If I recall right, he refuses to feed on humans, or does so only on the really bad ones (i.e., criminals that hurt other people). He's also quite broken by the earlier events in his life (Claudia's death, Lestat's fate,...).
Where the interviewer (and, presumably, many of the readers) sees romance and passion, Louis sees desperation, suffering, and torture/guilt by his vampire killer nature that makes him a monster in the eyes of his own humanity. This is the message he wants to send. He's not there for the food.