Binding energy of nuclei is the result of two players in the game - strong short-range nuclear force between all nucleons and long range electrostatic repulsion force between protons. Up to atomic mass 30 nuclei is "hungry for binding", meaning that overall nuclear force dominates over electrostatic repulsion, so adding more nucleons makes nuclei even more tightly coupled. (That's why building $\mathcal H$ thermonuclear reactor is a thing, because at low atomic mass numbers nuclei releases energy upon taking more "companions").
In the range of atomic mass $30-90$ is a relative stability island, where nobody dominates from this force pair. Adding or subtracting nucleons at this point doesn't changes binding energy much, because electrostatic repulsion is "on par" with strong nuclear force, so "things" are saturated.
Things change up the ladder from the atomic mass 90. Electrostatic repulsion between protons becomes a bit more dominating than strong nuclear force, so nuclei is becoming "hungry for divorce". Shooting some neutrons into such nuclei, especially with high atomic numbers like $\mathbb U^{238}$, makes high risk for such nuclei to split apart into more stable components. That's the principle of radioactivity (induced or sustainable, doesn't matter). Atoms in this range releases binding energy upon splitting apart, that's why having a nuclear reactor of $\text U^{238}$ is a thing.
