Note the jurisdictions at play.
These are different bodies. The EU regulatory agency is aiming to be conformant with the UN regulatory agency. They are saying "whatever policy the UN comes up with, we're going with that".
This is done because harmonization is good for business. What's bad for business is every State having a different standard that every company in those markets must learn and certify to. If you're trying to sell an EU vehicle in Ukraine or Brazil, and Brazil and Ukraine reference the same UN rules, you're all set.
This allows them to keep up with rapidly evolving technical fields.
It's like a "symlink", or in legal terms it's called Incorporating By Reference. For instance most US states and central American countries have adopted as their electrical code the NFPA's NEC.... rather than write their own from scratch like Canada did. Each State has a tiny list of amendments, but generally products can be built to a national market.
By contrast, the alternative is a "copy-paste" - for instance the nonprofit endowment law UPMIFA was developed by a nonprofit then copied, with occasional modifications, into 49 state laws.
EVs are a rapidly moving field. Technical innovations are flying fast, and responsible central bodies need to make good decisions. Things are ugly if they don't. For instance UL and CSA, who hand in hand write US and Canada rules, decided sufficient safeguards were in place on a special electrician's WiFi login for initial setup of EV wall charge units. Ontario regulators heard "WiFi setup from a phone", panicked, and banned it, making the whole Ontario market more hostile to EVs since most wall units use that feature.
Also, harmonization is good for trade.
When you copy rules, you incur a technical debt where your regulators must constantly check to keep your rules in sync. And this also increases the task load for any company trying to sell into your markets, which deters competition in and out - protects your markets but cages your manufacturers.
Such protectionism tends to be discussed harshly at trade conferences such as G20 or GATT. "We literally incorporate UN rules" (why don't you) is an excellent rebuke.
