Some Installers place sleeves to receive the cup when the installation is complete. If you are not going to place sleeves in concrete, they may move. You might as well place the cup in dirt by itself.
If you choose not to secure your cup with concrete, then it is crucial that you compact, re-compact by hand around the cup, and carve to make sure the area around the sleeve is smooth without any ridges from the sleeve protruding.
I have visited past installations spanning two decades, and cups placed in concrete were still in great condition, including the area around them. Cups placed in dirt couldn’t take the beating that a flagstick can do to the cup and its surrounding surface, especially when there is a heavy downpouring of rain the day before. Cups placed in concrete outlasted cups that were placed in dirt by far.