HTML+JavaScript-based statically hostable apps (eg. presentations) can't use paths as deep links, since there's no standard for simple static hosting or URL rewriting (even 30 years later). Oh well.
They also could use the query part on the url rather than anchor.
Lastly statically hosted doesn't mean no URL rewriting, they could again catch links to parts easily.
The poor UX of these tools is just a lack of will, not a technical limitation.
Then again hacker news should probably not blanket delete the hash in URLs either.