I think Otz was the "safe" pick for JP. Players knew him, JP likes him.
Then JH opens his mouth / gets the media and fan base excited. I am assuming the donors want JP to make a look at all the options and want to ensure that we get the best hire, not just the safe pick.
Also, this year ISU will need to fill 7+ scholarships - whoever is the head coach (hopefully that of a top 5 team), will not have a much time to devote to recruiting if they are focusing on Houston. Keeping Otz as the #2 and main focus is recruiting, then bring someone like JH in who has probably a 2-4 year window before heading to something bigger, then let Otz take over a program that is well established.
If Otz takes over now, he will have one good year and if he can't land the recruits - the program is back in the dumpster.