Here's why agar is a good choice:

* Solid at room temperature, liquid at high temperatures: This allows for easy pouring and sterilization of the media, but it then solidifies to provide a solid surface for bacteria to grow on.

* Chemically inert: Agar doesn't interfere with bacterial growth or metabolism.

* Supports bacterial growth: Agar is a good source of nutrients for many bacteria, but it doesn't provide a lot of nutrients on its own.

* Relatively inexpensive: Agar is readily available and affordable, making it a practical choice for many applications.

While agar is the most common base, other materials are sometimes used:

* Gelatin: A protein derived from animal collagen, but it can be broken down by some bacteria.

* Silica gel: Used for cultivating specific types of bacteria, like photosynthetic cyanobacteria.

However, agar remains the standard base for most bacterial culture media due to its versatility and affordability.