It's a hard problem. The reason it is hard is that they have to balance runtime size against the potential value of an addition, against increasing the complexity of the language (Combinatorially- for every feature they have to examine in detail how it interacts with every other feature of the language, which is a lot of work), friendliness to noobs, friendliness to old javascript fans, friendliness to java ruby and python people who hate javascript, etc. etc. For this reason they have focused mainly on features that can't be added with a library for this edition.

If you are interested, I wrote a URI parser myself, which can resolve relative URIs https://github.com/Breton/jsutils/tree/master/uriparser