>>13913977Evolution is random. A lot of the time the answer to why didn't evolution do this, is just "that is not what happened".
Why did i eat pizza yesterday, insted of eating pasta? That is just what happened.
Also some animals do use photosynthesis through symbiosis, especially in nutrient poor niches.
Over all, eating is far more energy efficient than photosynthesis. Animals often need to maintain high body temperature, larger cell turnover etc..