Its fair to say there are lots of factors, including football success. Its fair to say Currie (Weber) is the biggest.
The real issue is not unsold seats, its people just flat not coming. The attendance for all of the games so far is listed at 12K+ for each, so obviously K-State is counting sold seats and not bodies at games.
That said, I think its a bit unfair to Weber to throw him in now. The issues with Weber have been discussed enough and I get that. If you choose to not get seats because of him fine (again, most people obviously haven't). But he isn't really to blame because its not like he hired himself. He's here now and if he's the reason you don't want to come, the real reason is Currie so take all your frustration out on him. For clarification this doesn't mean I'm saying don't make fun of chicken nuggets, pizza, shrillness, etc. that's all fair game and part of the fun, "ya know".
I think its fair to say football success is a big part of people not showing up as well. I'd guess most people who have basketball season tickets also have football and putting in the investment of time, etc for football games and traveling (10K fans to Ft Worth) has taken its toll. Weeknight games against Lamar and a D2 school lag in general, its just going to be magnified even more for many with what they are putting into football right now. I'd guess come Big 12 play K-State will have 10K plus in actual attendance as long as the team is performing how most of us expect it too.
If Frank was still here the attendance would be higher, but I don't think it would be by a lot. Instead of 4-5K actual we'd probably have 6-7K, but its not like the place would have been full for ND, Lamar, and Ala D2.