Every SVN branch costs money, any system that cares about branch ancestry is expensive.
If me and Jim are working on two features on the same release and then I find that I need to integrate Jim's work in order to continue mine, Jim will need to merge his [incomplete] work into a common ancestor. If I am working on a feature in a completely different release, this "merge path" gets long and begins to cost money and carry risk. Jim hasn't finished his work yet; before any release can happen, Jim has to finish his work and merge the complete changes to all affected branches. If we can't wait for him to finish, then we're rolling back his changes and, oops, someone rolled back the same change on multiple branches.
Now we can't launch a hundred features because there was an interdependency between two.
If me and Jim are working on two features on the same release and then I find that I need to integrate Jim's work in order to continue mine, Jim will need to merge his [incomplete] work into a common ancestor. If I am working on a feature in a completely different release, this "merge path" gets long and begins to cost money and carry risk. Jim hasn't finished his work yet; before any release can happen, Jim has to finish his work and merge the complete changes to all affected branches. If we can't wait for him to finish, then we're rolling back his changes and, oops, someone rolled back the same change on multiple branches.
Now we can't launch a hundred features because there was an interdependency between two.