why was krypton destroyed

Krypton was destroyed in a cataclysmic event which is a pivotal element in Superman's backstory. The precise reason differs based on various iterations.

In the original comics, Krypton's fate was a natural disaster - essentially, Krypton became unstable and eventually exploded due to extreme geological conditions. These conditions were largely due to excessive mining and usage of the planet's core elements which led to its instability. This event further symbolizes man's greed and the consequences of exploiting nature's resources.

In DC's 1986 miniseries 'Crisis on Infinite Earths', another account of Krypton's destruction was given. Krypton's demise was linked to the hubris of the Kryptonians themselves. Krypton was a technological society, so advanced that it even mastered space travel.

However, their advanced technology caused a self-inflicted nuclear winter, turning Krypton into a wasteland. Meanwhile, the Kryptonians lived in domed cities, ignorant of the approaching disaster caused by the 'Anti-Monitor', a cosmic villain who feeds on whole universes. Unaware of the inevitable, those on Krypton continued their daily lives until the final moment when Krypton was destroyed, saving only baby Superman and sending him to Earth.

Alternatively, in the 'Man of Steel' movie (2013), Krypton's destruction is depicted as both an artificial and natural disaster. The planet was exhausting its natural resources, causing the core to become unstable.

More than that, the artificial population control and manipulation led the Kryptonian society to self-destruction. Jor-El, Superman's father, tried to warn his peers about the impending doom, but it was too late. The governing council refused to listen to him, contributing to the planet’s fate.

Hence, Krypton's demise is a tale penned by their own technology and disregard for nature, thus serving as a powerful and timeless moral caution.