Red blood cells don't have a nucleus because without the nuclease there is a larger surface area so the cell can exchange more oxygen as there is more space to carry it. And the nucleus is to do more with reproducing, and since the RBCs function is to carry oxygen around so they doesn't need it.
The blood cells don't need to have a nucleus. Since they don't have a nucleus, they can contain more oxygen-carrying haemoglobin. This enables the cell to carry more oxygen to be transported in the blood, therefore boosting our metabolism.
lazy ass blood cells
A Comprehensive Guide on Calibrating Oxygen Sensors