I don't think it is rare, though. Iowa has been 8-4 / 7-4 in the regular season since I was born. That's 37 years. That's a very long time. It's not rare - the vast majority of bowl eligible teams are 7 - 5 or 8 - 4. That's probably 1/3 of the teams in FBS or more, and certainly within 2 standard deviations of the mean.
The fact is that most non-basement division teams can, and do, schedule themselves into 6 automatic wins a season. They win at least 3 in conference, and 3 OOC. Iowa and some B1G teams choose not to do that, opting for a rivalry or nationally relevant OOC game.
Alabama, though, chooses not to do that. That isn't a judgement against them. It's a smart choice given their conference slate. But Iowa could decide to play three automatic wins and get to 8 - 4 pretty easily every year.
I actually think it's rarer to have a long period of terrible football in a big conference - because if you have any pride at all you fire non-performers until you get a good performer.
Rare is perennial 10 win seasons. That's top ten programs in the country. 9 win seasons is good - top 25. 8 win seasons are average programs - the Texas Techs and Cals of the world.
All I want is an perennial top 25 football team, in a weak division. Nebraska is down. Illinois is down. Minnesota is down. We should be making hay while the sun shines.