Dragon Ball had the triple pentagle distinction of being foreign, an animated adaptation and about Asians. Also a children's cartoon involving aliens and magic. It was doomed before it started. Taking a franchise from another culture is hard on its own. Do you keep faith to the original culture and possibly alienate the one you're making it for (in this case keep all of the Japanese traits and nuances, including an all asian cast) or do you change the ethnicity of the characters and culture to adapt it to the one you're offering it to (Americanize it so that it's relatable to Americans)?
Either way you do it, you'll piss off half the audience. The fans will love it for being "authentic" but the rest of the audience will hate it for not understanding it and ignore it. If you alter it then the fans will hate it for adapting it to an American audience and you risk the American audience "not getting it" because what made it good is literally lost in the translation. Or in the case of Hollywood, their incapability to adapt anything properly except by accident.
Look at the mess that was/is/will be Akira. Fan are very adamant it take place in Tokyo, with Japanese actors, and probably in Japanese. But they don't get that if they do it like that, American and European audiences won't be able to relate so readily to it.
Airbender was entirely on Shamalayan. He went with the usual Hollywood line of "best actors" for the job then promptly dropped the ball on every concievable aspect of it. I'm sure you could find good Asian actors for the roles but he didn't try hard enough. Even if he had though I suspect it still would've bombed. And you can bet there would be claims the actors being Asian "hurt" the movie.
And as promised, my response to the actual topic itself.
Hollywood is a very slow, cumbersome business that literally repeats itself endlessly. That's why we get so many sequels, franchises, reboots, remakes, ripoffs, spinoffs, etc. Very rarely will anyone in Hollywood take a chance on something new.
A good related example is female heroes. We've had Ripley since the late 70's and Katniss now and all inbetween that have been a scattering of female action stars. There are some notable exceptions but by and large Hollywood has stubbornly held that women can't hold an action movie, even in the face of oh yes they can.
More often the ones who take risks are on the fringes, independents, the upstarts or the big companies who have the money and a smaller subsidary to take a risk on something that won't directly affect them, then clone it endlessly if it's successful or write it off if it fails.
Some of the examples cited are poor examples. Spider-Man is actually Indian in the Indian version of the comic. It's tailored to that culture so there are changes to him besides merely being "brown." At his core, he could be black or asian or anything else but he's iconically white in North America and Europe. It's a byproduct of when superheroes were almost exclusively white, because predominately the comics were bought (or percieved as bought) by white children. Boys imparticular so they catered to that demographic.
It takes time and it takes effort to create a new superhero and I think rather than potentially alienating existing fans by radically altering the face of an iconic hero to be another ethnicity (and failing to adapt him/her on top of that to the big screen), it's better to create a new hero from scratch who is that ethnicity.
To make Spider-Man Korean for example, is to pander to making a Korean superhero for the sake of making a Korean superhero. It does nothing to make him different. There's nothing to be gained from it but plenty to lose, in the eyes of Marvel and Sony.
There is nothing obviously white about him on the surface but it would still be a major change to an iconic hero who has never been seen as anything else. And it's "appropriating" a hero for the sake of it.
That may sound racist, maybe it is in some interpetations but you can't deny it wouldn't mar the movie before production began. Whether you or I or anyone here says it wouldn't bother them (I'm being generous in saying no one here would be bothered, given the Johnny Storm can't be black debacle) it doesn't mean the majority of the audience wouldn't question it, and rightly so.
Why make him different? What does it do for the character? To justify changing him to Korean for the audience, you'd have to do something that makes him Korean, instead of just a white guy with a Korean face.
This applies to any character who has a firmly grounded background. Heimdall is interesting as he's a Asgardian "god" and yet he's not like the rest. He stands out like a sore thumb to the rest of a largely white cast. I have no problem with him being black, but only him and no others of note makes it all the more obvious he was "stunt casted" which is only tangentally progressive.
Hollywood should still be praised for diversifying. It's still a long ways off and has a long ways to go but like so many other things, it takes time, effort and a lot of failure before there is success.
Minority characters (and despite the claim it's offensive, it's definitely a step up from "colored" which I think the OP has lost the inference to) are increasing in prominence. Minority also meaning gay/lesbian and those of other ethnicities or religious beliefs.
I wouldn't expect a major shift in Hollywood but I can still see the shift happening and it's moving faster than it ever has before.
This also all ties into the audience. Movies are made to cater to the audience and the audience is still largely seen as white males for comic and superhero movies. It may be wildly inaccurate (I honesly have no idea what the true demographic is) but the perception is that it's still mostly white male so that's what we'll largely see until it becomes more accepted to see other ethnicities.
Which it is. It just isn't happening over night or perhaps in large strides for the next decade but it is still happening and it will get there.
