As depicted in Avengers: Endgame, losing half of the world's population in an instant would be disastrous. The world is built to sustain the current population. Who would take care of all the buildings, all the creations that this world has made? Families would be lost and destroyed, and the world would fall into despair.
Additionally Thanos has an absurd amount of resources at his disposal, in the Avengers films he is depicted as having a massive space armada and control over an absurd stretch of territory. Surely Thanos could use such resources to restructure earth, and other planets economic systems in such a way that would make them more sustainable. It is unclear as to why Earths population won't simply bounce back after the snap, even without the events of endgame, and the systems responsible for environmental desegregation still very much control the economies present in the MCU.