It sucks, yes, but that's probably how these people think.
the main reason is that this is not a reference implementations or "this is the app everyone must use" case but a "to see what is technical possible/practical" "research/POV" project
this also makes the "EU age verification app" title quite misleading
Which is a joke when you know that most phones in the wild are using an obsolete OS version (most of the time due to lack of software support from the manufacturer, but sometimes because some people just refuse to update because updates are in fact downgrades — looking at you iOS).