I can assemble ideas and communicate them just fine, but yes I also often brainstorm half-formed ideas with teammates. This is intentional, not a accident or because I can't think for myself.
It's a process that I (and others) find leads to better ideas quicker. Why waste time fully fleshing out an idea alone and only afterwards present it to others who might instantly see some flaw you overlooked that they could have pointed out at the beginning? It's perfectly fine if I throw something at you and you have no idea what I mean, and even better if you rephrase it to clarify what I meant because you probably just clarified it for me as well.
I have a feeling your response might be that I'm wasting people's time like that but I disagree. In person I can see what another person is doing before I engage them, so I obviously am not going to bother them if they are busy or focused on something else. I can always bring it up later at lunch or just whenever I notice they have a second.
Maybe that makes it more clear why this does not translate well remotely. It's tough to translate half an idea into text, and while that forces me to make it into a full idea first it's also slower. Remotely it's also impossible for me to know what they are doing before I engage them, so I would start breaking their concentration and wasting their time.
For me that extremely lightweight and casual brainstorming is one of the most important parts of having a team to work with.