Why? They still got a lot of the major concerts. They host other big events there, too. Having a niche and being known for doing something really, really well has a lot of value.
This is more from an outsider perspective. When I fly back to Nebraska, Omaha is not even close to the top of my list for places to show people. Hit the zoo and have some food and drinks later in the Old Market. That's quite honestly all they have to offer (for me). I personally feel they need to build on the offerings they have for the city (while building that niche).
You really don't know much about Omaha if those are your only highlights.