Question

Does anyone know why red blood corpuscles don't have nucleus

Answer 1

To maximize the space available for hemoglobin and to give the cell it's biconcave form that maximizes the surface area, so more O2 can readily enter the cell.

Answer 2

It is part of a larger organism i.e. humans and so it doesn't really need a nucleus. If it was a unicellular organism, the necessity would have been greater.