I tried to include these, but it wasn’t immediately obvious how to construct them from outside Scala without CanBuildFrom. If anyone wants to open a PR or even provide a few hints, I’d be happy to update the benchmarks.
Scala 2.13 greatly simplifies the external interface of the collections and no longer requires CanBuildFrom [1]. You may find them much easier to work with now.
[1] https://scala-lang.org/files/archive/api/2.13.0-M5/