In theory, they can. But JavaScript is based on the ECMAScript standard and that standard dictates what the language should implement. The ECMAScript standard is managed by a group which has processes by which features get implemented. Those processes can require a long time between the suggestion of a feature and the actual adoption of it as standard. Check out the TC39 proposals.
There are a lot of good reasons a language doesn't just adopt everything that seems like it would be helpful to anyone at any time. A language like JS needs to be backward compatible (don't break the internet), maintain a solid but sane feature set, and keep the idea of what the language is trying to be and how the language should grow.