> For example, erythrocytes (RBCs) don't have nucleus and mitochondria.

They are less of an outlier when you find out that they start out with a nucleus but pinch it off and let white blood cells eat it when they near maturity.

https://wi.mit.edu/news/how-red-blood-cells-nuke-their-nucle...

They also shed their mitochondria at about the same time. Both make more room for hemoglobin, optimizing them for oxygen transport.