I believe it's actually more complicated than that. Heyx3 is pretty lowly rated compared to other music shows at the moment despite having the golden air slot, so I'd assume they're aiming for bigger guests. Idoling!!! did appear on HaneTobi some time ago, though, and a second with the help of Masuno. It's also possible the amount of members might be a problem.
As for Hexagon, personally they're better off not appearing. Shinsuke wants his family, and seriously, it's like Zumi's 0 points never happened.