« Explained », surely, but that doesn’t mean the argument is compelling. I understand it when several « terminals » lead to several boarding areas and things can overlap. You mention VIE as a perfect example, and there are many others.

But in airports where there are distinct terminal buildings (CDG, JFK, LHR…), there is no need. Which means that in the case of CDG, with the exception of the new Terminal 5 which has distinction boarding concourses (some need to be reached by train, others not), there is no such need. You check in Terminal 1, you go to gate number x or y, which are necessarily in that terminal. You check in Terminal 2, you go to gate number x or y. And so on.

Alternatively, if one really is convinced that there have be no two gates with the same number in the entire airport, you could just prefix every gate number with the first number of the terminal. All gates in T1 start with 1xx, in T2 they are gates 2xx, and so on.

I agree with you, many people don’t think about certain things, they just follow signs. So they can just as well follow signs to « Gate 1xx » which would logically be in T1 or follow signs to « Gate 6xx » which would logically be in T6. There is no need to use those letters, which just add another layer of structure (fair enough, if you think that is needed), which has nothing to do with their location (that is just adding unnecessary complexity).

But in any case, there is no need for us to agree, ADP will do it anyway. Which will help some people, confuse some others, and I just take as another example how in France we love to over-conceptualise things which could be so simple and straightforward 🤣