It's a file format, there will be lots of uses.
Like it’s your site, exactly as it would be if it was delivered by your server just delivered by someone who already had a copy on hand rather than fetching a new one every time. This is what HTTP proxies used to do, what DNS caches and browsers still do. TLS broke web caches because TLS secured the connection instead of the content.
The most important issues is the 'lack of value' - not anything else.
Complexity compounds to imbue cost geometrically, we don't need stuff 'because', we need stuff that solves real problems.
If it doesn’t come with a benefit to you then it’s all good.
HTTP caches were always problematic from a business perspective. Great for downloading large binaries (installs) but problematic when they don’t expire as expected, or if content needs to change for contractual reasons.
It's not like you're forced to cache things if it doesn't work for your business case.
Web bundles changes this relationship so that anyone can cache sites if it benefits them to do so. If you share a link on Twitter or Facebook or Discord or Slack they can cache the page on their servers and deliver it through the connection you already have open to them.
Web Bundles also open the door for network-local caches that don’t require MitM or trusting the cache.