Why might components from Atlaskit not be displayed in Jira?

Question

JIRA

import SectionMessage from '@atlaskit/section-message';
import Button from '@atlaskit/button';
import Spinner from '@atlaskit/spinner';
import Toggle from '@atlaskit/toggle';
import { Label } from './label';
import React from 'react';

export default function HelloWorld() {
  const [excitementLevel, setExcitementLevel] = React.useState(0);
  return <SectionMessage
      title={`Hello, world${excitementLevel ? new Array(excitementLevel).fill('!').join('') : '.'}`}
      actions={[
        {
          key: '1',
          href: 'https://atlassian.design/components/',
          text: 'Browse more components to add to your app',
        },
        {
          key: '2',
          onClick: () => setExcitementLevel(excitementLevel + 1),
          text: 'Get excited!',
        }
      ]}
    >

      <>
        <Label htmlFor="toggle-default">Allow pull requests</Label>
        <Toggle id="toggle-default" />
      </>

      <p>
        Congratulations! You have successfully created an Atlassian Connect app using the <a href={'https://bitbucket.org/atlassian/atlassian-connect-express'}>atlassian-connect-express</a> client library.
      </p>
      <Spinner size={xsmall}/>
      <Button />
    </SectionMessage>;
}