No particular reason other than I'm used to redux.

My gut reaction when it came out was "it seems rather unwieldy compared to redux to have to manage client-side application state through graphql", but my gut reaction could be wrong, and I haven't actually tried apollo-link-state so this isn't really an informed opinion. Notably though, it feels think graphql is great for graph data, but pointless overkill for most global application state which isn't really graph data.