Hi @sayabannatole,
Per the official Adobe docs, the purpose of Asset Expiry is to deactivate/unpublish the published assets that may have licensing requirements. Hence it makes sense not to have that as an option of whether to deactivate or no.
OSGI component responsible for this functionality is - com.day.cq.dam.core.impl.ExpiryNotificationJobImpl which handles the send notification and deactivation logic.