Idioms have to be agreed upon (by the community) else they have no value at all. Shorthand only works if both people in the conversation understand what it means.
It seems like you are upset that the idioms came from the standard libraries (which is where I believe the initial idioms for Go, Java, and Python stemmed from), but you also have to give time.
Play was released in 2007 -- Java was released 1995. So it took a number of years for that change to take place. During the between time, idioms helped move java forward, make it understandable, make developers able to communicate via code.
Go was released in 2012 (v1), so of course a lot of the idioms are going to stem from the standard library -- we don't have two decades of Gophers moving the ball forward and agreeing as a community what the idioms are, they gotta start somewhere.
> Java programmers familiar with the circa-2004 idiomatic BS over-reliance of GoF patterns and deep class hierarchies created code that was "idiomatc Java EE" but difficult to undertand, overengineered, and inflexible.
Idioms are not static. Please stop using that as a strawman to tear down. Idioms rot. If they are not what the community currently uses, they are not idiomatic.
> People keep saying that, but most Go projects I've seen are made by only few of people, maybe even a couple. Plus, people complain about even single-developer Go projects being "unidiomatic".
Current use and design goals are not the same. Google developed Go to be used at (many-people) scale, even if it currently isn't (which I don't agree with: https://code.google.com/p/go-wiki/wiki/GoUsers). It isn't like Go can stop individuals from using it.