More often than not, it's either:

-a cursory glance by someone who doesn't have time to care

-a highly detailed critique from someone who will either be scooped or proven wrong, so they're looking for any reason to reject the paper, good or bad

-a grad student who puts in the effort but probably still lacks the experience for a good review

And if peer review actually was useful then the false cure for MS [0], arsenic-based life [1], or vaccines-cause-autism [2] would all be DOA and never been published in major journals to so much PR fanfare. Heck, most of Retraction Watch wouldn't be a thing [3].

[0] https://www.statnews.com/2017/11/28/multiple-sclerosis-paolo...

[1] https://phys.org/news/2012-07-scientists-nasa-arsenic-life-u...

[2] https://retractionwatch.com/2011/01/06/some-quick-thoughts-a...

[3] https://retractionwatch.com/

So "yet to be peer reviewed" means the study paper is closer to "random generated garbage text" than to "important insight".