What is the reason behind more severe proteinuria in nephrotic syndrome than in nephritic syndrome?
It is to do with the extend of the damage to the glomerulus. In nephrotic syndromes the glomerulus is damaged so that there is death of the podocytes. This happens to sufficiently high number of podocytes so that large proteins such as albumin and clotting factors can leak out causing large proteinuria. Damage to the basement membrane may also occur, such as in minimal change, where there is a loss of charge on the basement membrane.

In nephritic syndrome the damage is as a result of inflammation which does not lead to the same structural damage as in nephrotic syndrome, therefore there is not leakage of protein to the same degree.