Because we're probably looking at all our options. Martinez if I remember rightly was the favourite for the job last time but it still took a while before the club officially approached and interviewed him. Before that we interviewed to Neville, Stubbs and Ferguson internally and apparently spoke to Vitor Pereira and Ralf Rangnick as well to see how long our potential list was before deciding that Martinez was indeed the man we definitely wanted and focusing on him.
The board is probably putting the feelers out to the agents of several managers and seeing what response we get. As much as we'd all like the new manager in as quickly as possible but if we focus on one guy straight and it leaked to the media then it would mean showing our hand too soon.
