It was made for basically anyone who will watch it. You had action and humor that would appeal to kids while also incorporating more adult jokes and themes that only adults would get. It also meant that those same kids would picks up on those more adult jokes and themes when they came of age thus the shows maintain an enduring popularity. This is not particular to the DCAU, nearly all Western Animation works like this. That's why you have grown millenials saying that 'as a kid you relate to Spongebob but as an adult you relate Squidward the most'.