I’m not saying this is the reason, but smart coaches use the 2 deep to work on the set offense, the break and the timing. You need the true speed and quickness of your top athletes to create the rhythm and timing on offense.
Walkons are responsible for a couple of things; keeping the energy high in day to day practices and being an opponent. You want those guys who are excited to hit the court or weight room everyday, and force the top group to bring it, or they will make them look silly. More strategically, Walkons tend to fill the role of scout players, so you prefer if they have certain skills or traits that mirror some of those players you will be facing. They may not have the actual speed, or the ability to finish when they penetrate, or the strength. But if they can be a catch and shoot guy for weakside defensive work, or someone who can penetrate the lane to work defensive rotation, or even be a tall target in the post, that’s the type of person you look for as your walkons, and maybe JC isn’t quite what they are looking for. Upgrading your walkons isn’t unheard of.