Here's why:

* Size: Viruses are incredibly small, typically ranging from 20 to 400 nanometers in diameter. This is significantly smaller than the wavelength of visible light (400-700 nanometers).

* Light Microscopy Limitations: Light microscopes use visible light to illuminate and magnify objects. Due to the diffraction limit of light, they can't resolve objects smaller than the wavelength of light. This means light microscopes can't see viruses.

* Electron Microscopy Advantage: Electron microscopes use a beam of electrons instead of light. Electrons have much shorter wavelengths than light, allowing them to resolve objects at much higher resolutions. This means electron microscopes can "see" viruses, providing detailed images of their structure and shape.

In summary, electron microscopy offers the necessary resolution to visualize the tiny world of viruses, which are beyond the capabilities of traditional light microscopy.