I think you are asking the wrong question. I think the question should be Does Wilder actually want to fight Joshua? If you want to try wrap your head around why Wilder would refuse an offer like the one DAZN have offered him the only conclusion that fits is Wilder is ducking.
I think Wilder wants the fight but his handlers don't. They were cautious in his match making ever since they signed him from Goldenboy, they matched him up predominantly vs other Haymon fighters whenever possible as to not lose the belt even if Wilder should lose, Finkel refused meetings more than once to make the fight and it was Wilder of all people that emailed Hearn with an offer forcing his handlers to deal with it.