Product Owner: There are many reasons

1. Maximizing time for business return on investments: The product owner does not have to deliver the work or maintain the process. However, they are responsible for making priority calls and maintaining a backlog of requirements. 

This allows for a lot of focus. You can get more information about the safe product owner at https://prettyagile.com/events/category/safe-product-owner-product-manager/.

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2. A single source of requirements: No one in the organization needs to be consulted about a project's requirements. For a single point-of-contact, senior stakeholder requirements flow through to the product owner.

3. Changes in requirements can be handled by one person: Only one person is responsible for capturing and updating the requirements as the business changes.

4. The best compromise is achieved: Even senior stakeholders must trust the product owner in making the final decision. This helps align the business and allows for appropriate compromises in the best interest of the product.

Development Team: There are many reasons

1. A team of experts: Scrum teams can be explicitly called experts. This allows other roles to concentrate on their areas of expertise.

2. Scrum teams can be flexible to meet business needs. They adapt to any situation to build a product increment. Every decision should be tied to a business need. This gives businesses long-term and short-term flexibility and decreases effort wasted in favor of focused effort.

3. It is cost-effective and lean: Because of its small size, combined with the high level of expertise, things are accomplished with high-quality results with little technical communication.

4. There is less management required: Teams organize themselves. This allows everyone to focus on their own roles.