The path from SBT to Scala-IDE is well described in many places:
As a seasoned Eclipse user, I wondered the same thing. Amazed that no one seemed to be going that direction, I decided to roll my own project.
https://github.com/scalastuff/esbt
Install plugin, create or modify build.sbt and dependencies are fetched, project files updated.
It works for me, I use it every day. But it's not perfect or finished, and I'm not putting in a lot of effort in it at the moment. But do feel free to contribute!