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 initially, then bringing back a first attempt at consensus for proper and open scrutiny by national authorities. Then you send your delegates back to attempt to resolve any show-stopping issues and prepare final wording. Finally you ask each country's national government to ratify the final agreement. If really necessary, the national scrutiny/delegate negotiations cycle can be repeated first, though if that is happening it suggests the attempted scope of the agreement is too broad to be practical.
This way you would have a chance for people who were actually elected to influence the outcome usefully, without resorting to ongoing line-by-line revisions by thousands of individual MP, MEPs, US senators, etc. You just have to recognise that your delegated negotiators are not sent with the authority to make major policy decisions but only to reach a consensus that all parties can accept on areas where you are already broadly in agreement.
If they aren't able to do that, such that they can come back with a proposal that each country can clearly favour overall with no deal-breaking terms, then again they probably shouldn't have been trying to form such a complicated agreement about such controversial areas between so many different parties in the first place.
And how do you think every country came up with their agendas for the negotiations?
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?
And how do you think every country came up with their agendas for the negotiations?
I don't know, and I don't think you do either, because it was done in secret with no open, democratic debate. You can tell this from the fact that many elected representatives who participate in the normal democratic processes are among those complaining about a lack of access.
One reasonable process might be having each country send their appointed representatives to negotiate initially, then bringing back a first attempt at consensus for proper and open scrutiny by national authorities. Then you send your delegates back to attempt to resolve any show-stopping issues and prepare final wording. Finally you ask each country's national government to ratify the final agreement. If really necessary, the national scrutiny/delegate negotiations cycle can be repeated first, though if that is happening it suggests the attempted scope of the agreement is too broad to be practical.
This way you would have a chance for people who were actually elected to influence the outcome usefully, without resorting to ongoing line-by-line revisions by thousands of individual MP, MEPs, US senators, etc. You just have to recognise that your delegated negotiators are not sent with the authority to make major policy decisions but only to reach a consensus that all parties can accept on areas where you are already broadly in agreement.
If they aren't able to do that, such that they can come back with a proposal that each country can clearly favour overall with no deal-breaking terms, then again they probably shouldn't have been trying to form such a complicated agreement about such controversial areas between so many different parties in the first place.