[barrkel]

Hash maps and trees: fine. What about database interfaces (e.g. a JDBC/ODBC/whatever equivalent)? What about HTTP servers - even the minimal declaration for what a synchronous request handler might look like? How about threadpooling - if you have multiple libraries that have parallelizable work, you certainly don't want multiple threadpools each thinking they have X many cores to work with, and you don't want the user to have to partition these things either - that's not a happy problem.

All things you can delegate to third parties, but not without lots of cross-talk and confusion until things settle down to winners and losers, which may be a long time in the future. Indecision can be costly.

Consider standard library profiles, with progressively higher levels of abstraction supported. It's the right decision for creating a good ecosystem. C and C++ took decades to build consensus on the more complicated libraries, and C++ eventually grew a pseudo-standard library in the form of boost to centralize efforts, simply because it is more efficient that way.