You have the base virtual machine installed, and then the app just needs to ship the code itself.
You could even ship with an "install script header", like "if this isn't installed, offer to download and install it". I imagine a lot of us have seen these kinds of installers before.
For example, if there were a Debian package for either of those, all apps leveraging them would just declare that same package a dependency and you'd have a single system-wide install for the large binary everyone keeps complaining about. (AFAICT there is no such deb package for any of the above.)
The JVM (and apparently qbrt) is designed to be shared, apps are expected to use the installed system version of the VM, though if the packager wants they can include a specific version to use.
I wish it were easy/possible to get Electron apps to share things, it bothers me that Chrome, Discord, and Slack almost certainly could share most of their hundreds of megabytes.
https://www.npmjs.com/package/nwjs
and electron:
It's not completely bonkers. It could be possible to make a web installer that checks for node and electron and downloads them if necessary. Nobody seems to do that though. Every electron app bundles electron. At least every one I've seen
That plus scarring from browser differences over N years.
Of course it's still totally possible, but there are probably gotchas that aren't obvious if you're mainly a web developer.