For me, my interest in this started in a lunch queue. During a conference in Manchester a couple of years ago, I overheard the two people ahead of me listing all the different ways they had come across intending to convey the concept of widening participation. It was a surprisingly long list and, musing on other similar examples, got me thinking about how we ever understand one another at all, when we use multiple terms to describe one thing and between us ascribe multiple meanings to one phrase.
Added to that, the change of terms that seem to be sometimes no more than fashion, trying to establish a vocabulary that will last is no small task. The thesaurus that goes with it, built on the phases currently in use, is a way of dealing with those variations of phrase without prescribing how people should express themselves.