Why does overall system inertia naturally decrease as grids incorporate more solar and wind farms?

Answer

Inverter-based resources do not have massive rotating physical masses

Traditional synchronous generators provide inertia through their massive rotating masses; as grids incorporate more inverter-based resources like solar and wind, which do not spin physically, the overall system inertia naturally decreases.

Why does overall system inertia naturally decrease as grids incorporate more solar and wind farms?
storageenergyenergy storagegridgrid stability