The issue here is that we aren't saying anything about the real problem. You can radically scope software down. That will indeed make it more secure. But you will stop making money. When you stop making money, you will stop being able to afford the developers who can write secure software (the track record on messaging software written by amateurs for love is not great). Now we're back where we're started, just with shittier software.
It's a hard problem. You aren't wrong to observe it; it's just that you haven't gotten us an inch closer to a solution.