Here's why:

* Standard Units: The ideal gas law equation uses standard units for its variables. Volume is typically expressed in liters, pressure in atmospheres (atm), temperature in Kelvin (K), and the amount of substance in moles (mol).

* Consistency: Using liters for volume ensures consistency with other units in the equation, leading to accurate calculations.

While other volume units might be used in some applications, liters are the most common and standard unit for volume in the ideal gas law.