Why is Nightcrawler's soundtrack so upbeat?

It seems that the writer, Dan Gilroy, wanted to bring out the humanity of the character rather than just portray him as a sociopath. He seems to have intended the music to be subversive, as he informed Howard to create "uplifting" music, rather than the "nightmarish score" that was probably expected. James Newton Howard told The New York Times:

But the goal was to use music see the scene from Lou’s eyes — that is, as a moment of great possibility for his career. “It really becomes an anthem of potential for his tremendous success,” Mr. Howard said. A more triumphant feel was in order.

“I think people could take that as an intentional miscue, but it really isn’t,” he said. “It was designed to orient people into understanding where he’s coming from as a character. And I think it’s key to the success of the score in the movie.”

Dan Gilroy told Consequence of Sound:

“It’s the music in his head,” Gilroy points out. “It’s a bit of a magic trick: As the music is creeping into your own head, it’s creating this feeling of eagerness and climbing the ladder and succeeding and trying and not giving up, all while you’re watching this maladjusted behavior get rewarded — it cements you to the character and his quest.” It’s a surreal effect that romanticizes Lou’s ambitions, making his story feel curiously tangible. Gilroy adds: “We’re alongside him in the car, and we’re on this exciting, adventurous experience. It’s awakening all the same things that you might feel when any of us are pursuing a goal.”