Samsung was probably testing OneUI Core 4 to low-end devices, including the A01, and encountered issues that made some devices not eligible.
They could either optimize OneUI Core 4 more for phones like the A01 or they could not include the devices that ran into issues for the update.
Do note that the list may or may not change and the A01 is not the only device not eligible for the Android 12 update despite Samsung promising this device to have at least 2 Android updates.
