Let's be honest and have some claps for jQuery, it's been a dominant JavaScript library after its official release in 2006. The main reason is to get this much audience is that it's just makes JavaScript code much shorter and it has some crazy built-in functions and features. The craze to jQuery accelerated when most of the CSS frameworks and JavaScript library for animation and plugins, started using jQuery including bootstrap 3.
The downfall
After the release of the JavaScript ES6 update in 2015. Vanilla JavaScript just became more powerful. Updated features like arrow function, higher-order function all of them are currently an essential part of JavaScript. This was the time when modern JavaScript Frameworks like react.js came into life and started getting more popular as those were more then just a library and they are classified as JavaScript framework. These modern framework make full use of JavaScript and recommends developers to use vanilla JavaScript for operation.
Bootstrap drooping jQuery ?
In a recent leeks it came that bootstrap 5 the next major update of bootstrap will be dropping out jQuery and adopting vanilla JavaScript. Reason behind, it was "modern JavaScript Frameworks and libraries". As these modern framework uses vanilla JavaScript then jQuery just ads as an additional library which just does nothing except running bootstrap. And Its my personal opinion that using vanilla JavaScript runs way more faster then jQuery. This is will be relief to lots of developer if bootstrap drops out jQuery. Because lot of developer loves bootstrap but does not uses jQuery. So jQuery just ads as an additional tool in a project which is of no use from developer side.