DC has plenty of lighthearted stories as well. Just look at the Teen Titans comics and animated series, and also Teen Titans Go!. Like Spider-Man, they show young heroes balancing teenage life with superhero work. Or look at the Harley Quinn animated series, which portrays a humorous, satirical take on the heroes and villains of Gotham.
But aside from that, levity isn't always a good thing. If you focus too much on entertainment value, you lose out on exploring a deeper storyline with a meaningful plot and themes. Summer blockbusters are a fun watch, but they're ultimately meaningless. The Marvel movies have been criticized for generic plots, overdone comedy, and shallow action.