Always possible that it's the standard commercial software company reason: They do know about it and have a P2 bug tracking it, but the team that maintains that code has 5000 other things to do, and it never gets fixed.

More likely it’s that 48 kHz is a more sensible default, since the majority of non-music digital audio is sampled at 48 kHz, almost anyone who cares about potential audio artifacts introduced by resampling is going to be using an external DAC, and (from an Apple-centric viewpoint) almost anyone concerned about the energy consumption of music playback on their MacBook is going to listen to music on their iPhone instead.