I think they made it this way for a good reason. Saving FPS. Because when you switch modes to an external camera, it basically switches off all the internal cockpit rendering which makes up a huge chunk of CPU processing power to simulate the internal cockpit instruments systems, displays refreshes, and animation.
You don’t want your sim to both render Exterior Model (which has impressive quality to begin with) and fully rendered interior cockpit at the same time. That will bring your CPU and GPU down to its knees trying to process all of them simultaneously for something that you might not notice.
That’s why by having separate modes, the sim can switch off completely the stuff that it doesn’t need. So the interior becomes a very simplistic model with barely any instruments or simulations. While at the same time, on cockpit view, it doesn’t render the external model at all to focus on rendering the interior cockpit instruments. That way, you can have playable FPS on both modes.
If let’s say they take your advice and just give you what you want, no more camera separation, everything is real time and at the same time. If you end up having 5 FPS, will you still be thankful to the devs for removing the separation? It’s annoying, sure… But annoyance is still better than unplayable.
My point is, we don’t know why they make design decisions that way. But I’m sure they have a good reason to do so, and we just have to live with it, and make some adjustments and work around them.