As soon as a person is added to the approval process, the system sends an email to this person when the approval process starts. If multiple people are added for approval, the first person receives an email, followed by the second, and so on. This allows control over who receives the approval information in which order.
Therefore, if a person has not received an email to approve the hiring request, it is very likely that it is simply not their "turn" yet.
Note
For multiple hiring requests with the same approvers, it may happen that this sequence is "skipped." For example, if approver C logs in and is supposed to approve only one hiring request but decides to approve four more (even though approver A should be next), they can do so. Approver B might then think they were skipped because they have not yet received an email. In this case, the system will still send the email only after Approver A has approved.