And why, for the love of god, does it have a separate numbering scheme?!

Because they want the ability to reference other vulnerability sources - like JVN - and not just CVE.

The EUVD service builds upon the CVE system and vulnerabilities in the scope of the CVE numbering service receive a CVE. In addition, the EUVD data aggregates and enriches the vulnerability information and lists an EUVD ID on top of the CVE when new vulnerability entries are created. To allow further cross referencing, the CVE identifier and additional vulnerability identifiers are listed when available. -https://euvd.enisa.europa.eu/faq

And because, you know, standards.