Planetary magnetic fields influence atmospheric evaporation from space weather, yield insights into planet interiors, and are essential for producing aurorae. The most direct way of measuring magnetic fields on exoplanets and their brown dwarf cousins is by observing exo-aurorae at radio frequencies. However, a quasi-stable and non-auroral quiescent radio component accompanies all known examples of substellar exo-aurorae and provides an alternative means for assessing the physics occurring in substellar magnetospheres. The presence of incoherent nonthermal radio emission requires both a source of radiating electrons and magnetic fields to accelerate these electrons. Thus, the absence of quiescent radio emission from a single object cannot distinguish between a lack of strong magnetic fields or magnetospheric plasma. In contrast, examining the occurrence rates of quiescent radio emission can potentially reveal how brown dwarf and ultracool dwarf radio activity depends on various fundamental properties such as effective temperature, mass, and age. Here, we present the first such statistical studies of quiescent radio emission from brown dwarfs and ultracool dwarfs and discuss implications for substellar magnetospheric physics.