Here's why:

* Heterotrophy means obtaining nutrients from organic sources. This includes consuming other organisms (either dead or alive) or their byproducts.

* Autotrophy, the other main way of obtaining food, involves making food from inorganic sources. This is primarily done by plants through photosynthesis, and some bacteria can perform chemosynthesis (using energy from chemicals). However, autotrophy is less common in bacteria.

Here's a breakdown of common ways bacteria obtain food through heterotrophy:

* Parasitism: Living inside or on another organism and obtaining nutrients from that host.

* Saprophytism: Decomposing dead organic matter.

* Chemoheterotrophy: Obtaining energy from breaking down organic molecules.

* Photoheterotrophy: Using light as an energy source but still needing to consume organic compounds for carbon.

Therefore, while there are various types of heterotrophic bacteria, obtaining food from organic sources is the most prevalent way bacteria acquire nutrients.