There are a multitude of factors.
In basketball your only recruiting a few kids (or so) each year. Coaches have more time to coddle 10 or so players they would like to sign and then you end up with 2 or 3 really high ranking players and a mix of others. In football your looking at 100 or more recruits every year, probably significantly more than that. They are spread out all over the country, they encompass a lot more positions on the football team. Just the sheer time to evaluate and make first contact with these players is daunting in of itself.
Too many other programs have more money to invest in facilities to wow recruits, money to hire people at all levels to identify, make contact, stay in contact, and help market the program. We can argue back and forth about our crowds and how or why they don't come, how upset they are that we moved big games to different locations, and all the other b.s. The fact is the crowd at the dome is marginal compared to the top programs. That might be generous. If we want to have a top 10 recruiting class year in and year out we better have a packed *cking dome when 5 star kids come to visit when it's cold as hell outside. We don't. Other programs do. Chandler Jones this year when asked by a reporter something about the SU fans responded that "we didn't really have a lot of fans". That pretty much sums it up.
I realize other schools like Ped St., ND, Michigan, Ohio State, etc. don't play in the south but geography will always have some impact on getting certain players that want to play in what they believe is a more desirable location. Now, if your going to play in Michigan maybe you wouldn't mind as much when there are 100K fans at the game. We've lost players each of the last few years who seemed to want to go to southern climates.
These are just a few variables. None of these are program killers but people are expecting top 10 classes, you better have a real special program with lots of potential "assets" for recruits if your going to haul in top 10 classes year after year after year. We don't and there is nothing wrong with that, we can still be competitive. There are few programs that have the ability to recruit at that level consistently.