It's not clear that there is an issue.
Is the lack of coupling actually a lack?
The lack of coupling between the two side-sticks to provide feedback between the pilots is, intuitively, a lack in the interface.
We are used, in the physical world, to being able to feel what another person is doing through the things that we're manipulating, the machinery and tools we operate together.
However, flying a plane is not like carrying a ladder up a narrow staircase, or riding with someone on a tandem bike. That kind of implicit bodily feedback isn't part of the Airbus cockpit system.
Cockpit communication is supposed to be explicit
Instead, the communication is supposed to be explicit, so the pilots say what they are doing when operating the controls. Introducing physical feedback into that environment might seem like an enhancement, but in fact it would be the opposite: it would be the introduction of a source of doubt, that draws habit and practice away from the explicit communication around which the system has been designed, towards an implicit form of communication.
Even implicit communication requires verbal confirmation
It would then be necessary to introduce also a new system under which the pilots would decide whether their explicit verbal communication is now in operation ("I have the controls"), or the implicit physical communication (you feel the other pilot doing something).
Now there is a new burden! As well as deciding what they should be doing with the controls, the pilots must also decide whether they will be prioritising explicit/verbal or implicit/physical communications - two things to manage.
And working that out will require explicit verbal communication, so they may have well just stuck with that in the first place.
And if implicit physical communication is allowed to have weight, they still need explicit verbal confirmation of it, because that's what pilots always do. By the time I have asked my co-pilot "WTF are you doing with the stick and why?" it's already later and more stressful than if they had said in the first place that they were taking the controls to climb over an unexpected mountain.
It's not a lack, it's the removal of something unwanted
Implicit communication through the side-stick is not a free gift of additional useful communication. In the Airbus cockpit system, it's the introduction of something dangerous and unnecessary, that would require extra cockpit management and would harm communication in the cockpit.