Does he though?
If he really wanted to, he'd know by now that he needs to leave and earn it.
I suspect he would like to manage us one day, but there are one or more of a number of things which may be more important to him, possibly including:
1) Financial security - he has a job right now. A relatively secure one it seems. The life of a manager is an insecure one. I seem to remember that he was made bankrupt going back a few years. Perhaps his and his family's financial security are more important to him than his designs on the top job.
2) Everton - Cheesy one but perhaps he loves being part of the club. There's always the possibility that given a choice between managing in the lower divisions and coaching at his beloved Everton, he chooses the latter.
3) His home life - Barring a spell in Spain after he packed up football, Duncan has lived here for most of the last 30 years. He married a scouser. It's not inconceivable that at the age of 50 he doesn't fancy uprooting and living elsewhere
And probably a host of other stuff I can't be bothered to think about.
I'm not convinced he wants the job enough to do what he needs to do to get it. I'm sure he'd do it if he was offered it, but he wouldn't be the first person at our club to say he wanted to manage the club but to ultimately stay put in another role. I seem to remember Unsworth coming out with the same stuff when he had his 2nd caretaker spell. Incredibly, I seem to remember Joe Royle resigning from his role here because we overlooked Unsworth for the job.