Same reason Wisconsin does. Not a big urban population to pull from (and Wisconsin has better population than Iowa). Also a big reason the "rankings" never look good for a Wisconsin and Iowa is they are not afraid to take 2* kids they have evaluated themselves as much greater than some Rivals guy ranked them.
Both Iowa and Wisconsin pulled the trigger on Martin after they had him at camps. They didn't care at the time that he was a 2* kid that Rivals barely had on their radar. If he would have committed to one or the other, they would have taken it, and felt great about it, and Martin stays a 2* kid as he then doesn't camp for Rivals and blows up. That type of recruiting, especially with Iowa/Wisconsin kids that get no exposure is gonna keep your rankings low. Another example of this is Nathan Stanley. Stanley camped with Iowa, and Iowa instantly offered and made him priority #1. They didn't care that at the time he was a 2* or low 3* nobody. Sure Rivals re looked at him and bump his * rating up, but Iowa was there first. Same with Mansell. The staff is out recruiting, and they run across him, watch him throw, evaluate him and offer him. At the time he was a low 3* nobody. He has a good Sr. year and he gets re evaluated by Rivals and now he is a 5.7 3* guy. Yet sometimes they don't re evaluate at all, they only did with Mansell because he did lots of 7 on 7 camps.
The simplistic view of well we have the 9th rated B1G class so we are the 9th best period, end of story we are gonna suck is just stupid. There is very little to no difference between the #30 class and the #45 class. You hit on a Stanley, or Wadley, or a King or a Jewell or a Watt, or a Biegel, or one of the countless other under recruited/evaluated kids that come out of Wisconsin and Iowa then there you go from #45 to #30 in an instant. Iowa and Wisconsin trust their evaluations skills and more time than not, they are right. If a kid camps with one of those two teams and earns an offer, you can be damned sure the kid can play, and if that was a Rivals camp, they would increase their rankings with the performance they showed at that camp.