I pointed this flaw out repeatedly in the Rust forums when there were discussions related to improvements that could be to crates.io. They made it very clear that "everyone understands" that crates themselves are the "source of truth", and that nobody should be doing security reviews by going to GitHub or wherever.
So what happens in reality?
Precisely what you just did. People instinctively click the source repo link, and browse around in the GitHub history view to "see what happened".
Sigh.
It's like trying to explain to someone that the cargo lift design of the Death Star is dangerous without handrails. Then someone points out that when you signed up to be a Stormtrooper on the Death Star there was a clause in the contract (page 537 paragraph 7) that clearly states that it is your responsibility to avoid fatal falls due to precipitous ledges.