I've heard the same excuses from ML engineers before introducing tests there, embedded engineers, robotics engineers, systems engineers, everyone has a reason.
The real reason? It's because writing tests is a different skill and they don't actually know how to do it.
Oh that's crap. I've been a software engineer for over 30 years. I love tests - I preach testing at my current place of work. I've also worked in games for about a decade. Testing in games is... not useless, but very much less useful than it is in general software engineering.
I have no experience in the gamedev industry. But based on the number of bugs I see in games, plus the size and quantity of post-release patches, maybe your perspective here is because you're not trying to hit a level of reliability at launch that would justify having more tests?
The real reason? It's because writing tests is a different skill and they don't actually know how to do it.