What are the disadvantages of Vanilla.js?

The disadvantages of Vanilla.js are: lack of built-in structure, increased development time for complex projects, and manual handling of advanced features. Vanilla.js entails that the developer would write more code to help manage tasks, say state and component organization, or event handling, which may make the application not that scalable.
Vanilla.js also does not include such reactive data binding, templating, and Virtual DOM updates out of the box, which React.js and Vue.js provide for easier UI management. Large applications without a framework will be more difficult to maintain and scale because there is no default structure or tooling to organize code and optimize performance.