Requisition escalated to higher approver

Hi

A purchase requisition was raised with the amount within the allowable limit of the approver but it was escalated to another approver higher up the hierarchy. The original approver is the custodian of the account to which funds will be drawn from.

Why would the the requisition be escalated upwards if the amount if within the approver's limit? What are some of the things I can check for?

Thanks in advance.