Earlier quoted context omitted.
How can every country's MPs change the agreement? How does this work in practice? Have you thought this through?
Individually they can't, of course, but consulting them as a group is reasonable for something you expect every country to implement. Without the backing of the elected national government, you have no democratic mandate to change national laws or update national policies to reflect your international agreement. One reasonable process might be having each country send their appointed representatives to negotiate init…
Are you absolutely sure that you know how the current process works? Or you just read some articles here and there and concocted the story in your head?