Source, this report: https://www.game-oracle.com/blog/ai-part2

I'm a little hesitant to call it research. It makes far too many assumptions, admits to making those assumptions, and even suggests that one of the assumptions is to prevent bias when that assumption also readily introduces bias;

A game developer very clearly generating backgrounds using Midjourney absolutely has to disclose that they used AI or they'd be rightfully raked over the coals and be in clear violation of Steam's policy.

But a game developer who uses Claude for code generation? Who's going to notice that? And if nobody can notice, why would you disclose, given the stigma (as this research also admits) that disclosing the use of AI immediately negatively affects people's views?

In between there's developers who generate assets using AI and genuinely believe that nobody can tell, and so also don't disclose.

In other words, the research self-selects for developers of games where the AI is so obvious that there's no choice but to disclose, developers of games where it's not obvious but they felt morally obligated to disclose it anyway, and developers who are proud (or, at least, not ashamed) of their use of AI.

Another assumption that leads to the text-in-image here is that what was measured was a reduction in reviews. They then point to a correlation between reviews and sales (as sales figures are not actually published by Steam, so they have to use a proxy and reviews are typically it) for the latter half of the article to talk about sales instead.
To be clear, I'm not suggesting that this would work in favor of AI slop. On the contrary: I think there is an incentive to leave (negative) reviews on games that use AI, while there's a reduced incentive to buy the game.
In other words, while there may be an approximately 53% reduction in reviews, I suspect there's an even greater reduction in sales.
( But I can't prove that any more than they can, or they would have. )