They have better basketball fans for sure, but for good reason since they have fielded a lot better teams in the last 25 years. Back in the 80s and 90s Carver was rocking. Been a long time since then, but it can happen again with the right AD and coach. Carver is rocking for wrestling meets and does really good for women's bball. So I know it can happen again for men's bball.
It's the teams. If the Iowa women can put 15,000 in the stands for a big game than it's not the fans or the arena, it's the product. The Gustafson teams had great attendance to so it's not just the Clark draw but she does (obviously) make quite a difference.
I do think that Iowa football fan loyalty and ISU basketball fan loyalty is sort baked into the cake for both schools these days. I don't think either is a "use it or lose it" like Gophers MBB. 20 years ago William's Arena was the best fan venue in this pro sports town, rivaled only by the Gopher hockey crowds which where crazy. Today, not sure how they even bring it back. Might be the perfect time to burn it all down and build a new arena, hire a coach that doesn't suck and rebuild their fan base.