I completely agree that Signal could very much use a third-party client, especially on the desktop. That being said if they want to push their cryptocrap they have to keep a strong control on the clients because third parties are likely to just ignore that functionality altogether, hampering adoption.

I'm not saying that's the main reason for them to exert such a tight control on the Signal ecosystem but it shows how damaging that move has been: now you can't really exclude an ulterior motive for them refusing to integrate with third parties. It damaged the trust I had in the project.