The size is a fundamental constraint of optical technologies, because it is related to the wavelength of light, which is much bigger than the sizes of semiconductor devices.

This is why modern semiconductor devices no longer use lithography with visible light or even with near ultraviolet, but they must use extreme ultraviolet.

The advantage of such optical devices is speed and low power consumption in the optical device itself (ignoring the power consumption of lasers, which might be shared by many devices).

Such memories have special purposes in various instruments, they are not suitable as computer memories.