Using EUPL is mostly a way to signal that you want to use a license grounded in EU law, not in US law. That's at least the way I've looked at it.

if the EUPL actually closes the SaaS loophole (first time i'm hearing about it though) in a legally grounded way i can see it being used by people outside the EU who say the AGPL is unenforceable/is actually nonfree/is too hard to actually comply with