There's no rule that says the language/library/framework divide has to lie where contemporary scripting languages put it. In PHP and ColdFusion, HTML is part of the language; in Ruby or Python it's usually relegated to a templating library; in Javascript the DOM is usually a library and it's bad practice to build up HTML strings (in 2015, at least; in 2008 it was good practice to build up HTML strings, because it was orders of magnitude faster than using the DOM). In Matlab or R, statistical and linear-algebra functions are part of the language, while in Python they're a library. In C++, strings, hashtables, and arrays are part of the standard library (or not even that, in early versions), while in Python & Ruby, they're part of the language. In Lisp the language parser is part of the language; in Rust, C++ (under Clang), Python, and Go it's part of the standard library; in many other languages it's not available at all.

There are certain best practices that have emerged for general purpose languages. Imba is not a general purpose language; it's explicitly meant for web programming, and makes sense that it would build common web programming functionality into the language itself.