I agree completely with your second paragraph. But I think that your first paragraph sells short what a fight with Orcus in the Abyss means - if it's just a very dangerous boss fight, in my view the GM has done something wrong.
This is true, but it's also true of most boss fights. To the original question of "what player wouldn't want to go to the Abyss and kill Orcus?", the answer I propose is "not everyone." Replacing "orc chieftain" with "Orcus" doesn't automatically speak to every player; yes, you can raise more interest in it by working hard at context, but you can do that for every enemy. Which is why epic power levels, when they aren't enough on their own, need some extra attention to be made appealing.
What I think is missing to an extent from WotC (although they hint at it in the campaign outlines that they sketch in Underdark and The Plane Above), is an account of how epic D&D can speak to the personal concerns of the players (as developed and expressed through their PCs actions in the gameworld) while at the same time connecting to the metaphysical and otherworldly aspects of the game.
Quite agreed, especially (as I see it) given that epic tier has several obstacles to overcome that other tiers don't, such as mechanical complexity, a reduced focus on the mortal world and mortal NPCs, and a "climax" that extends over ten levels.
Okay, I can certainly see that as a possible scenario. But I can also see alternatives. I have played at least one "affable rogue" in recent-ish history (tha character was a Bard, but he was definitely a "rogue" in the non-class sense!), and even though he was deeply invested in the "mundane" world as played, I can quite see making a conversion to be interested (as both character and player) in "epic" play. Given an evil god meddling in what he holds dear, and a realisation that "these 'divine' and 'immortal' types are no better than us!" combined with rage that "this upstart thinks he can destroy what I have worked for, just because he has some jumped up label of "god"??" I can easily see such a character drawn into epic quests. And, as a player, the thought of what an "affable, worldly rogue" might get up to when exposed to the planes beyond - now, that would be an adventure!
Sure. But the major obstacle that stops me is being told "Now you're going to spend an entire third of your character's gaming career with no significant interaction with that mortal world you hold dear." The focus on taking things extraplanar is a big stumbling block for many characters who enjoy
this world; there are many Azzagrats, but only one Ladona. For some players, yeah, that's not a big obstacle. For others, it's close enough to insurmountable that I think it
really needs addressing.
Leaving aside that pretty much every story ever written has some element of evolving past a personality flaw, it seems to me that every D&D character (specifically D&D, as opposed to all RPGs) has to be built with a motivation to adventure. And I think that's all that is really needed to get into epic play - as long as the player is interested.
I think you have to leave aside the literary example precisely because (a) most players don't build their characters in such a fashion and (b) well, just speaking for myself, my players who do also base their characters on literary examples that never go into the "epic" over the course of their stories. These are the players who see their stories as something to be resolved in the mortal world. And they're also the ones who refine their motivations to adventure more carefully, often tying them specifically to the world. If a player wants to become the head of his House over the course of his career, leaving it behind to go tool around in other planes for ten entire levels may not be as attractive as simply saying "Goal achieved" and retiring.
Understood - but the painting of the Epic tier as only being 'bashing demons to save the world' is a failure of marketing, in my view, on WotC's part. Especially when, as pemerton points out, they have products that show other possibilities to good effect.
Yes. It should be more. And if there is really to be a Field of Dreams effect of "if you build it, they will come", you need to address the players who aren't as interested in saving the world.