Why would criminals use these kinds of apps rather than e.g. Signal?
Based on the article, Encrochat didn’t sound like a fully legitimate company and may have been run by criminals as well. The part I found interesting is how these vendors often block competitor apps and services from working on their phones, essentially requiring everyone to use the same type of modified phone. This made life a lot easier for investigators once the network was penetrated.
I doubt that provides significant value. Cameras aren't too hard to disable yourself, just use black tape. They probably didn't disable to microphones, which arguably provide at least more valuable information than a camera. They removed the GPS module, but you can probably get the same info with better accuracy by using wifi + cell phone signals. All in all, I think those "features" are just there to make criminals feel better.
If you have evidence that unencrypted data might be leaked from Signal (except by a rootkit on the phone, tampered update or by someone having physical access to the phone) you might have a real scoop on your hands and you should contact project zero or someone for a bounty and then a journalist so you can bask in the glory.
If you don't have anything I suggest abstaining from writing in a way that suggests that until you find something.