God damn you retards for dragging me into posting about fucking 2020's nu-Marvel. GOD DAMN YOU. This whole redditarded "but killing half of the universe wouldn't solve anything" is low IQ and you know better. Just literally removing half the eaters isn't the real point (although it would take a lot longer than 10 years to get populations back up, places like Ukraine for instance will never ever recover in real life, as an example).
The larger point is that nobody knows what happened. Nobody knows how or why except a handful. Just a sudden wrath of God that deleted half the universe, leading to plenty and abundance. Even the relatively small percent of the universe that Thanos dealt with personally back when he was just flying around killing half of a world by hand had been having droves of people follow him and worship him as a god. But most would never know what happened or when it will happen again. They would live in fear of more divine retribution for a billion years to come.
That's what would have happened everywhere. Every planet would think the Heavens themselves (or whatever their local equivalent belief is) had done it, and governments would make sure that anyone who pushed back to overpopulation would be fucking killed. No world, even ones that were just Stone Age isolated feral worlds, would lack a priesthood-like leadership from cradle to grave making GODDAMN SURE nobody tempted Fate or God again. Every dude who decided to rail some girl would be worried that this would be the baby that would get half of the universe instantly, inexplicably vaporized all over again.
It's not just practical to kill half of the resource-using organisms. It's about sending a message.