why List<T> use array is not from ArrayPool

[zms9110750]

I have seen array pooling used in other class implementations, which indicates that version updates can modify the API implementation. So currently not using array pooling is intentional.
So why? Isn't using array pooling beneficial or even harmful?

[huoyaoyuan]

Array pool has its own overhead and limits.

First, each type requires a new pool of the type, which is somehow cost-ful. That's why only array pool of very common types (byte and char) are used in BCL. In fact List<T> even avoids Array.Empty<T>, which has a cost of generic instantiation.
Using array pool also requires proper returning management. For list, the only controllable time for returning is expanding.

[DL444]

What I understand is that ArrayPool<T> and MemoryPool<T> are mostly useful for temporary buffers that the renting code owns, usually in place of stackalloced buffers when stackalloc can't be used for whatever reason. Outside of these scenarios, the renter really has no good way of returning the buffer - you don't want List<T> to be IDisposable, do you.