the game is intended to be played from the perspective of your character. This means that traditional third-person views are out, and any potential external views will have to be filtered through that perspective.
FD have already "forced" everyone to use an external view in their outfitting section. Perhaps they did not believe there was enough scope in the HUD to allow for it, but that is definitely a third person view and not from the perspective of your character.
Having said that, I do agree with you, but I will change your emphasis...
The game is intended to be played from the perspective of your character.
When you are in an external view, you are not so much 'playing' the game but pausing to admiring its beauty. These views have no HUDS, frames or anything to spoil the view - thats the whole point.
In this fan video , at no stage would you say Neon Raven was actively playing the game even though he was playing the game. He was effectively in spectator mode, attempting to position himself in a manner to capture beautiful scenery free of cockpit infrastructure. The game made it very difficult for him to do this and he was forced to take these shots from his canopy view, where the fewer visual obstructions exist - thus emulating an external view.
Even earlier, FD released similar videos themseves which clearly demonstrate how much more beautiful the game is when seen from an external viewpoint. This video is important because it summarises this entire topic well.
The video comprises of 5 scenes, all taken with from an external viewpoint.

The 3 frames above involve exploring and trading, and it is here that I believe external views would be beneficial in improving a gamers experience by heightening the visual beauty of the game. That is, the scenery is not needlessly interupted or destroyed by the cockpit framework. Immersion for some is improved, and for others, remains unchanged as they would not select this view anyway as it is a choice - thus, there are no disavantages here to anyone, but there are advantages to some. A no lose situation.

The next 2 frames above involve combat scenarios. Now here, things are completely different. Although the shots look more beautiful than if they had a superimposed cockpit, I believe there is a disadvantage in engaging an external view while in such combat scenarios because there is no time or purpose to appreciate visual beauty in the midst of a fight - which is different to you watching someone else (as in this video). In combat mode, with the weaponry, strategy and manovering to worry about, not many players will be stopping to smell the flowers.
No-one is trying to force anyone to use external views (apart from the pre-mentioned outfitting screen). Immersion for ED remains exactly the same for an individual as the same cockpit view remains in place. All people are asking for is an option to select an external view.
The beauty of Elite was that it could be played in so many different ways by different people with different playing styles. If you didn't like combat, you could focus on trading and still get the same pleasure from the same game because if offered you that flexibility - that choice.