Incident and Service request priority

Answer:
Although it sounds logical, it's not necessary that incidents (or service requests) with high impact must have high urgency. For example, there is an incident or service request affecting reporting module in your ERP, part that deals with financial year reports. Although complete business of the company is in danger (like, reports submitted to the governance can't be made, or can't be made correctly), there is still plenty of time to resolve this.
Or, there is a service request, or bug, affecting some parts of the intranet (e.g. a part of intranet that affects all employees but does not a ffect business operation).
You can learn more in the article "All about Incident Classification" https://advisera.com/20000academy/knowledgebase/incident-classification/