The problem with HTML is that it's not a stable format. Will a browser in 2028 be able to render those pages correctly ? What about 2038 ? If the content needs to be available for a longer time PDF/A would be a much better choice than HTML.
Not a stable format as in still gets updated? Very few formats are stable by that yardstick, and PDF certainly is not one: https://www.iso.org/standard/63534.html
> Will a browser in 2028 be able to render those pages correctly ?
Correctly as in "in a way which can be consumed", most certainly. A modern browser can consume and render 20 years old websites just fine.
> If the content needs to be available for a longer time PDF/A would be a much better choice than HTML.
It really is not. PDF is a very complex format and an absolute bear to manipulate and extract data from.
Why not? Modern browsers can still render pages from the 1990's.