Field-induced ferroelectricity in (doped) hafnia and zirconia has attracted increasing interest in energy-related applications, including energy harvesting and solid-state cooling. It shows a larger isothermal entropy change in a much wider temperature range compared with those of other promising candidates. The field-induced phase transition occurs in an extremely wide temperature range, which contributes to the giant electrocaloric effect. This article examines the possible origins of a large isothermal entropy change, which can be related to the extremely broad phase transitions in fluorite-structured ferroelectrics. While the materials possess a high entropy change associated with the polar–nonpolar phase transition, which can contribute to the high energy performance, the higher breakdown field compared with perovskites practically determines the available temperature range.