Because RunCommandCursor returns a cursor, we know the command is a read command, so it would help users who implement custom read commands with it to have it implement retryable reads.

This is encouraged by the retryable reads spec, which says:

Any driver that provides generic command runners for read commands(with logic to inherit a client-level read concerns) SHOULD implement retryability for the read-only command runner.

In the short term, it would also help tools/mongomirror implement custom find commands without implementing their own retryable read logic.