Similar issues occur in train travel.
In a lot of places you can book a compartment completely (for sole use) even if you don't physically occupy all the slots. (This is like CE)
In the same sorts of circumstances you can also choose to *not* book all the berths and risk having a cabin mate. Often you get sole use anyway, but it's obviously not a defined benefit (this is like Y).
But in some parts of the world (I'm looking at you India) it doesn't matter if you have booked all the berths or not, the way people think means that any available space will be used whether it is properly allowed or not. And there is really nothing you can do about it, people just don't see what your problem is even if you have paid for it. Whilst this change in attitude is at its extreme in some places, you can clearly see that there are fundamental differences in the way people think that apply not only to whether you can\could\should change seat or allow it, but to almost everything in life.
I term these differences "roundhead" and "cavalier". Roundheads see the rules, cavaliers see the opportunity.