It's not just the US but yes the lack of trust is a major component. Everyone seems to have a horror story of how someone made it through and sucked and caused problems. It's bizarre how traumatic that is allowed to become because people don't get rid of those bad apples quickly. And it's funny how people over-index on this in the engineering realm when it's a much larger problem in management.
But there's also a bunch of other dynamics going on. 'Geek machismo' is a very non-trivial one. Other's are akin to hazing. One friend of mine described one value of very high bar hiring is that people in the bubble can (go back to) assume that the colleague is smart, etc. rather than assuming people are stupid/incompetent until proven otherwise--and that can be a good thing from the culture/sociology standpoint.
Just make "Assume good intent" a part of your culture, and that will accomplish the same thing (and as a bonus, make your company a much nicer place to work).
When building your own culture, of course. However, that also misses the fact that there's also the larger context of e.g., silicon valley "norms". So much cargo culting of behavioral patterns from unicorns, the spread of the various "mafias" from them as they go to other companies, etc. Add in the various management level sillinesses and it's a harder problem to solve for most people than your comment implies.
But there's also a bunch of other dynamics going on. 'Geek machismo' is a very non-trivial one. Other's are akin to hazing. One friend of mine described one value of very high bar hiring is that people in the bubble can (go back to) assume that the colleague is smart, etc. rather than assuming people are stupid/incompetent until proven otherwise--and that can be a good thing from the culture/sociology standpoint.