The reason is that QUEEN is, by definition, a very restrictive measure -a 'good' translation must be similar to all human references according to all metrics.
as to portability across test beds (i.e., across language pairs and years), the reader must focus on the cells for which the meta-evaluation criterion guiding the metric set optimization matches the criterion used in the evaluation, i.e., the top-left and bottom-right 16-cell quadrangles.