Because certain things are woven into DC's DNA that aren't woven into Marvel's, things like sidekicks forming teams. DC is also really good at heroes who run fast and Marvel isn't but that has nothing to do with this post.
For the longest time Marvel was uncomfortable with the teen/sidekick hero concept. Look at it this way, for awhile Marvel's most popular teen hero was Spider-Man and it's attempt at a teen group were the...X-Men. Neither were legacy. It just felt like DC was the legacy folks and Marvel was too cool for that.
It still feels like Marvel is uncomfortable with the concept.