When you import a Scala project via an SCM integration, Snyk uses the build.sbt manifest file to determine dependencies.
If your dependencies are declared in an external file, or in a format that is unsupported by Snyk, the project will only find the scala-library dependency as default.
Please see Git services for Scala projects for more details on supported declaration formatting.
See also Why has Snyk not found my dependencies or all manifest files?