I don't understand your question. You are asking "why" you can choose something. What exactly do you mean?
Sorry,
it's :
Why I can't choose element Datas of my Cluster ?
Ahhh. Completely different message.
If you have a wire with data that does not have a label and bundle it into a cluster, you can access it by the regular unbundle, but cannot unbundle it by name because it doesn't have a name. The solution is to give it a name.
Two ways to do it. Use a typecast on the brown wire to typecast it to the same type, but using a constant that has a name in its label. The other is to wire a cluster constant into the top of the unbundle and make sure all the elements in that cluster have a name in their label.