it's because "opening" an html file only means it remains open for a few minutes and then the file manager gets garbage collected and if you close the web brows

it's because "opening" an html file only means it remains open for a few minutes and then the file manager gets garbage collected and if you close the web browser and reopen it, the page is not accessible. They intentionally gimp local file access, because they make money from selling cloud services. My threat model does not include nation states/carrier attacks, the information I hold is not considered illegal yet.