Were I a betting man, I'd say the prohibition, or advice, not to initiate a go around once the reversers have been selected is as much to do with human factors as with engine management.
Lots of runway can be used stowing reversers and then selecting TOGA power, if on a shortish runway grief could be the result. On a long runway, one would probably get away with it.
By prohibiting the practice, it avoids the last minute "it seemed like a good idea at the time" decision.