Depends who you ask. Illinois is a big state and geography plays a big role in who individual fans see as our rival. IMO, IU checks more boxes than the other rivals (border state, bad blood between past players/coaches, historically competitive with one another in conference, etc.).
But to your point, I also know the rivalry isn't really reciprocated by most IU fans, which is what prevents this rivalry from being one of the marquee cbb rivalries.
Not putting you in this bucket, but many Hoosier fans see IU as being too superior to Illinois to consider us a rival and instead consider UK their rival. However, similar to the IU vs UI rivalry, Kentucky doesn't consider IU a rival (in a 2022 poll, IU wasn't even listed as one of their top 6 rivals). I was talking to a former IU cheerleader a few years ago and she made some kind of comment about how IU always beats Illinois. Until I sent her actual proof to the contrary, she was adamant that our head to head records weren't even close. So, this air of superiority from IU fans also contributes to the rivalry from our point of view.