You don't appear to realise how few people are like you. There are 12 confirmed kills of DG. That's it. That's not even 100 players. No company that wants to stay in business is going to create content that only 100 people ever see (ie everything past DG).
The fight is still far beyond the capabilities of at least 95% of the playerbase. It is hard by any reasonable definition of the word. If you don't find it hard, then you're just very unusual.
If the fight is beyond people's capabilities..then the course of action is simply to improve their game, or suffice to clear hard mode..until the next tier releases and kell dragon gear drops on easier fights.
Nightmare mode, again, is not 'everyone can do it immediately' mode.
The entire concept of top tier raiding is to provide a true challenge and thus attract players who want that kind of challenge. If people cannot clear content and quit the game (which in my experience has never happened with anyone I've ever raided with)..then I dunno, sounds like a personal issue to me - I play the game for a challenge though, and most, if not all of people I've played with appreciate that as well.