Here's why:

* Blood's primary function is transport: Blood carries oxygen, nutrients, hormones, and waste products throughout the body.

* Energy production happens in cells: The process of energy production, called cellular respiration, occurs within the mitochondria of individual cells.

* Blood delivers fuel for energy production: Blood delivers glucose (sugar) and other nutrients to cells, which are then used as fuel for energy production.

In summary: Blood plays a crucial role in delivering the components necessary for energy production, but it doesn't produce energy itself.