It's actually always been this way even since game dev teams grew beyond a handful of people. The size of the needed team starts small as the project starts, then ramps up as it continues, and then right after release you have a ton of people with suddenly (unless you've done very careful and difficult planning) nothing for most of them to do. And so, the standard answer is to fire the majority of them.
I have no idea what mixture is going on now of standard game industry behavior vs. now-standard tech layoffs vs. something new going on with games-industry layoffs specifically. But the trope of the game shipping, and then everyone instantly getting fired, has been a standard joke-not-a-joke in the games industry for decades.
I agree with you insofar as it is standard practice in the games industry, but that doesn't make it any less effed up IMO. Not only because it sucks for the game devs, but also because it means that studios are constantly annihilating their own institutional knowledge: "The person who fixed those bugs the last time? Sorry, they got fired in the last round of layoffs."