This is because many concepts are specific to particular domains, and for many words their most likely meaning in context is strongly correlated to the domain of the document they appear in.
the senses of a word ¢ are each assigned a ranking score which sums over the distributional similarity scores of the neighbours and weights each neighbour's score by a WN Similarity score (Patwardhan and Pedersen, 2003) between the sense of ¢ and the sense of the neighbour that maximises the WN Similarity score.