Because he’s effusive and can’t help himself.
"I don't want to talk too much about 'Ant-Man,' I get superstitious."
But as this is Edgar Wright and he is a thoroughly lovely and enthusiastic chap, of course he did…
As many Marvel aficionados will know, Hank Pym, the first Ant-Man, was a scientist who also invented the uber-robot Ultron but with the Avengers facing off against said angry android in their sequel, Wright explained quite simply why Ultron will not appear in his film:
“It was never in my script. Because even just to sort of set up what Ant-Man does is enough for one movie. It's why I think Iron Man is extremely successful because it keeps it really simple. You have one sort of - the villain comes from the hero's technology.
It's simple. So I think why that film really works and why, sometimes, superhero films fail -- or they have mixed results -- because they have to set up a hero and a villain at the same time. And that's really tough. And sometimes it's unbalanced.”
He then addressed his approach to a successful origin story:
“You know, when I was younger I used to love Tim Burton's Batman. I was like 15 and even then I was aware, "This is really the Joker's film." It's like, the Joker just takes over and Batman, you really don't learn too much about him. Comics have years to explain this stuff and in a movie you have to focus on one thing. So it's about kind of streamlining, I think. Some of the most successful origin films actually have a narrower focus.”
He also explained the attraction of making an origin story about a character that who is not a superstar of the Marvel canon:
“I think there's something in that it's a lesser known character, there's hopefully more license. For the one percent of people who are like, "Wait, Hank Pym would never do that!" there's 99% going, "Who's Hank Pym?" So, to me, the source material is great but it also frees you up to be like: I'm going to make a movie. The movie is not going to represent 50 years of Marvel comics because that's impossible. But I'm going to make a 100 minute movie -- or 110 minutes”
Ant-Man will be released in 2015.
Source: The Huffington Post