Why wood class-8 truck manufacturers install the air cleaner under the hood and what concern of having an air cleaner mounted this way in relation to power?

Why wood class-8 truck manufacturers install the air cleaner under the hood and what concern of having an air cleaner mounted this way in relation to power?
Installing the air filter under the hood instead of the outside would give less air flow and hot air from the engine, which would raise combustion temperatures and reduce power.