Booking concerts for HLSR is an art form - lots of budgets, logistics, and egos that go into it. Leroy Schaffer did it for years and knew so many of the touring acts' agents so sometimes he'd get a sweetheart deal or the performers would take a smaller cut since it "was for the kids". It was easier when one agent repped several of the artists - an agent might have 6 or 7 of their performers all play the rodeo in a year. Easy for the agent, the performers, and the show.
They've had years when a lot of judges from The Voice or American Idol all played the show - easy one-off gig when they weren't touring and same management companies.
Money is highly confidential - you can imagine a band getting 250K to play only to find out the next night's act is getting 400k.
This year the show took a hit because so many regular acts and wishlist acts were already playing highly lucrative festivals. Those artists don't want to play the same city twice.
Timing is also everything - rodeo has totally lucked out when some artists agreed to play rodeo and were at the very top of their game - Aldean, Luke Bryan, Clay Walker, Garth. Really no one creating a huge buzz like Cody Johnson or Parker McCollum last year. Rodeo must have signed the Oliver Anthony deal right when that song was hot - hoping there'd be some momentum there but a lot of legacy acts would've been much better choices.