Why do we still shoot 23.976 if NTSC and PAL have been replaced?
23.976fps still exists because it's a standard. Cameras became designed to shoot it, non-linear editing software suites were designed to edit them, and devices were designed to play them. Even though NTSC went away, cameras still shot in 23.976fps. Even if they could shoot a flat 24fps, it causes issues in the edit room.
Putting 24fps footage on a 23.976fps timeline will have some issues but can be mitigated by being slightly slowed down or with pulldown. However, you will run into issues with multi-camera setups and syncing audio, hence this
discussion about editors complaining about audio sync drifting.
In the end, 23.976fps still a standard because if cameras switched to 24fps, it would cause issues in the edit room, and if editors used 24fps timelines, it would give pretty much everybody after them in the pipeline a hard time. Even if everybody could adapt to 24fps, most delivery standards are designed for 24fps anyways, so it'd have to be converted back to 23.976fps at some point in the pipeline, therefore it'd make it much less of a hassle to just shoot at 23.976fps anyways.