> However, that compatibility also weakens its own copyleft
Keep in mind that within EU the GPL's copyleft is as strong as EUPL's or LGPL while at the same time EUPL takes into account network access like AGPL. In practice though, software is distributed outside of the EU and while GPL relies on local laws to "maximize" its copyleftness, EUPL specifically refers to either the EU country of the developer or Belgium if the developers from outside the EU, where the laws do not distinguish between static or dynamic linking (check "More details on the case of linking" from [0] about license compatibility). Also FWIW while FSF suggests that "license hopping" (i.e. changing to some compatible licenses from EUPL to something else) weakens the copyleft, a European Commision lawyer who worked on EUPL has commented doing so would be copyright infringement because the purpose of the compatibility list in EUPL is for interoperability (so that multiple projects with different licenses can coexist) and the purpose would matter in court.
Though in practice since software is often distributed outside of EU, e.g. to US where (it seems) such distinction does exist, people do respect (L)GPL's dynamic vs static linking requirements and from a worldwide perspective EUPL is something like LGPL with a dash of AGPL (making some program functionality available even remotely is considered as distribution). Or in other words, EUPL is basically AGPL within the limitations of EU law.
Keep in mind that within EU the GPL's copyleft is as strong as EUPL's or LGPL while at the same time EUPL takes into account network access like AGPL. In practice though, software is distributed outside of the EU and while GPL relies on local laws to "maximize" its copyleftness, EUPL specifically refers to either the EU country of the developer or Belgium if the developers from outside the EU, where the laws do not distinguish between static or dynamic linking (check "More details on the case of linking" from [0] about license compatibility). Also FWIW while FSF suggests that "license hopping" (i.e. changing to some compatible licenses from EUPL to something else) weakens the copyleft, a European Commision lawyer who worked on EUPL has commented doing so would be copyright infringement because the purpose of the compatibility list in EUPL is for interoperability (so that multiple projects with different licenses can coexist) and the purpose would matter in court.
Though in practice since software is often distributed outside of EU, e.g. to US where (it seems) such distinction does exist, people do respect (L)GPL's dynamic vs static linking requirements and from a worldwide perspective EUPL is something like LGPL with a dash of AGPL (making some program functionality available even remotely is considered as distribution). Or in other words, EUPL is basically AGPL within the limitations of EU law.
[0] https://interoperable-europe.ec.europa.eu/collection/eupl/li...