Some software exists to "bridge the gap" for deficiencies in other areas of the software ecosystem. Javascript date api really sucked from 2002-at least 2016 (arguably still does? haven't really followed) and so these libraries come in to close the gap. Similar to JQuery.

Moment can be thought of as an instance (or build) of the iterative development of a strong usable, robust and bug free javascript api for dates. It's just that moment is the major release version that is still extremely popular but is a dead end in terms of design. Eventually the end goal is a solid, community agreed upon standard lib and in between versions (moment in this case) should be obsoleted while also not breaking existing code bases.

But read the attached article, it does a much better job of explaining than I do.

As the author says, the library caters to a language that is no longer in use - aka. javascript 2010 - and keeping up with the evolution of javascript would be making breaking changes, which have been accomplished by other projects by now. What would be the point?