Heroku is generally used for hosting APIs and other webapps that does not require file storage , due to the ephemeral filesystem of heroku we can't write file to the dyno.

Hosting a Static website is very simple , add an empty index.php file in the repo and Heroku thinks that its a PHP Web app and setups Apache for serving your files. you should name the home page of your static site as index.html and It will work