Sure, but there's a fact of the matter: It's not that we don't value the experiences or well-being of dead ancestors; it's that we hold that they do not have any experiences or well-being — or, at least, none that we can affect with the consequences of our actions. (For instance, Christians who believe in heaven consider their dead ancestors to be beyond suffering and mortal concerns; that's kind of the point of heaven.)

The "expanding circle" thesis notices the increasing concern in Western societies for the experiences had by, e.g., black people. The "narrowing circle" thesis notices the decreasing concern for experiences had by dead ancestors and gods.

The former is a difference of sentiment or values, whereas the latter is a difference of factual belief.

The former is a matter of "ought"; the latter of "is".

Slaveholders did not hold the propositional beliefs, "People's experiences are morally significant, but slaves do not have experiences." They did not value the experiences of all people. Their moral upbringing specifically instructed them to not value the experiences of slaves; or to regard the suffering of slaves as the appointed (and thus morally correct) lot in life of slaves; or to regard the experiences of slaves as less important than the continuity of the social order and economy which were supported by slavery.