Task-form-embedded-react Example SpringBoot issues

I was able to run the task-form-embedded-react example on Spring boot application by explicitly adding the following scripts to html file.
script src=“https://unpkg.com/react@17.0.2/umd/react.development.js
script src=“https://unpkg.com/react-dom@17.0.2/umd/react-dom.development.js

But Facing issues in code while adding the css or validations.
The major problem is about how the html is rendered. Why are we using React.createElement only to create or render the elements?
Why can’t we use simple HTML tags as we can do in any other React project?