Welcome to Scala 2.13.1 (OpenJDK 64-Bit Server VM, Java 11.0.6).
Type in expressions for evaluation. Or try :help.
scala> val b: Byte = -1
b: Byte = -1
scala> b.toBinaryString
res1: String = 11111111111111111111111111111111
Likely a combination of pragmatic reasons, among them that, while the RichInt method simply delegates to Java’s java.lang.Integer, there’s no such method on java.lang.Byte.