In the EU there is the "reverse charge" mechanism for VAT when commerce crosses country borders, and it is often used for defrauding EU countries / governments.

The invoicing standard is an attempt to mitigate reverse charge fraud by gathering more machine-readable data. Some countries even demand that b2b invoices are sent to the country, which then dispatches a copy to the recipient.

Knowing this background, it's pretty clear why the EU is making it mandatory.

Personally, in the abstract I like the idea to mandate the use of an open standard, I think we have way too many inefficiencies from treating many things as text documents that could be data structures. I don't like this particular standard though, it's bloated and the result of a typical top-down process.

I much prefer it when there are competing standards for a while, and one or a couple of winner emerge on technical merits. THEN I have no objections to a regulatory body picking a standard and mandating it.