Here's why:

* Resolution: The resolving power of a light microscope is limited by the wavelength of light. This means it can only distinguish between two objects that are at least about 200 nanometers (nm) apart.

* Size of Bacteria: Most bacteria are between 0.5 and 10 micrometers (µm) in size, which is within the resolution range of a light microscope.

* Smaller Structures: Structures smaller than bacteria, like viruses (typically 20-400 nm), organelles within cells (often less than 1 µm), and molecules, are too small to be seen with a light microscope. These require higher resolution techniques like electron microscopy.

Therefore, while a light microscope can reveal the shapes and some internal features of bacteria, it cannot resolve the details of smaller structures.