There are a few libraries out there that have been designed to go obsolete. For example, the Polymer project is planning that much of their codebase will eventually go away, as the shims they provide for Web Components gain better and better traction in browsers.
jQuery is much the same. It was designed and inspired by the browser wars in the late 90’s, early 00’s - the “bad old days” when cross-browser, cross-platform was a pipe dream. John Resig envisioned a toolset allowing users to use the same selection mechanisms, DOM manipulation, CSS manipulation, etc - regardless what browser they were on. Things like
$.ajax() were a powerful precursor to the modern
But jQuery was designed to play nice with other libraries, and eventually, to obsolesce. It was never intended to be a permanent fix: it was hoped that, eventually, the various browsers would come closer to a common implementation. And, by and large, that has happened.
jQuery was also a great tool for those who wanted to learn to code so very badly - and I know many many people who did just that. Learned to code, very badly. It never really required you to know how to write clean, elegant code (though it did support that). Some of the most hideous libraries of spaghetti code are directly children of jQuery.