Have one conglomerate force everyone to do better. If each country acted independently, each country is incentivised to not think about the bigger picture and act in their own short term interests.
This was my main reason for voting in.
These are not made-up examples.
And it's not just health or industrial standards, the EU forces a bunch of legal and human rights onto countries as well, many EU countries have gotten repeatedly and rightfully dinged over various deficiencies.
If each entity acts in their own self-interest — which nations very regularly do — then you get worse results for every individual.
For instance this quote from the Wikipedia page:
https://en.wikipedia.org/wiki/Hydraulic_fracturing_in_the_Un... https://en.wikipedia.org/wiki/Hydraulic_fracturing_in_the_Un... "A majority of the EPA's Scientific Advisory Board advised the EPA to scale back proposed toxity testing of fracking chemicals, and not pursue development of tracer chemicals to be added to frack treatments, because of time limitations. Chesapeake Energy agreed with the recommendation."
Conglomerations of power benefit people with power the most. That can be a positive or a negative depending on what policies those people want to pursue.