Very surprising that the Kotlin JS standard library is bigger in size than the Kotlin standard library for Android (about 500 KB)
Firsrt, you are measuring unminified version of stdlib-js. You can apply something like uglify.js (we use webpack + uglify.js plugin in our internal development) and then get code size closer to 500 Kb.
Second, Kotlin stdlib was initially designed for Java, where there are classes like ArrayList, HashMap, etc, and what Kotlin JVM does is aliasing its collections to Java collections. There’s nothing with similar interface in JS world, so, for compatibility reasons, we had to write our own collection library, which contributes to stdlib-js size.
Why are the Kotlin JS team not making any efforts to reduce the size of the Kotlin JS standard library?
The Kotlin JS team is not making any efforts since there are tons of work is should do as well, and it simply has no time to do something with code size. Please, be patient, and in some future releases you’ll get a way to reduce stdlib-js.