The current spec says that

An embedded node MUST NOT, itself, use a reverse property.

I am wondering why this behaviour was chosen?

It seems reasonable to me to explicitly allow this behaviour.

For example, the following snippet would produce the following when applying the toRdf algorithm:

{
  "@context": {
    "rel": {"@reverse": "ex:rel"}
  },
  "@id": {
    "@id": "ex:rei",
    "rel": {"@id": "ex:value"}
  },
  "ex:prop": "value2"
}

<<ex:value ex:rel ex:rei>> ex:prop "value2".

As illustration, I have implemented this behaviour into jsonld-streaming-parser.js behind the rdfstarReverseInEmbedded flag.