Yeah, this is a holdover from where LLMs grew out of: academia. "Technical report" is what you reach for when you don't want to compare to actual competitive baselines.
What this is an instance of is Google's approach to academic publishing of releasing a paper that contains almost no actionable information, but which is considered important and publishable solely because it came from Google and therefore is used in industry. This has been exhibited many times before--e.g. see the original Spanner paper, which was so light on details and confusing that they needed to release a followup paper several years later to explain what the system was even using the atomic clocks for!
I should have worded it better, in hindsight.
This is (IMO) quite different from, e.g., the cases of academics publishing misleading benchmarks, which is more often just being wedded to a bad idea because you spent years of work on it and your position is at risk if you didn't end up outperforming existing approaches. Often I can still get a lot out of papers with misleading benchmarks, even if what I get is "don't try this technique, it doesn't work." Whereas I frequently get nothing at all out of Google publications. If I had to describe the way Google seems to view academic publishing in one word, it would be "marketing"--it's advertising for people to either come work at Google or use their products, not something written with the intent of advancing the wider state of the art, or even the less noble goal justifying the time and money they put into whatever they're writing about.