It’s no mystery why “mainstream” characters created in the 1930s/40s were white. And, arguably, they should
still be white for “period” representations (where the action is set in the past). But the superhero genre typically and continually updates its mythos to the “present.” Thus, for example, the Christopher Reeve version of Superman was born in 1948; the Tom Welling version was mid-1980s. So with each update and modernization, there’s less reason to be obligated to the norms of prior decades - including racial “norms.”
Now, with certain characters, their race is said to be
intrinsic. Black Panther is one such (obvious) example. And it’s argued that Bruce Wayne is another - on the basis that the Waynes are a venerable New England family with “old money.” Ergo, they’re white. But, ultimately, the Waynes’ wealth is just an expedient to explain how Batman is able to acquire his fantastical tech. So if the fictional biography were simply rewritten to “new money,” the Waynes
could be black (though without a name change, perhaps not Latino or Chinese
).
In any case, it doesn’t seem like there’s been a mad rush to “race swap” most classic/iconic characters (notwithstanding rumors about James Bond). For instance, all recent versions of Sherlock Holmes have been white (including the two “contemporary” re-imaginings). Likewise: Superman, Batman, Wonder Woman, Green Lantern, Shazam, the Flash, Green Arrow, Supergirl, Batwoman, Daredevil, Jessica Jones, Iron Fist (!), Wolverine, Iron Man, Thor, Captain Marvel, ...etc.,
ad nauseam...
So in this light, changing the race/gender of
supporting characters (and only a few at that) represents a fairly modest "revisionism."