I see your point and I suspect Dyche would only use him in an emergency, but maybe you recall people complaining about us getting rid of Simms when DCL got injured at the start of last season.We needed a goal. He had him on the bench and didn't use him.
Why keep him then?
Well DCL is still "injured", Danjuma has just come back from an injury, which leaves us with Maupay, so do you not think it prudent to retain Cannon just in case hes needed in the next 2 weeks?