I don’t think that’s the only reason. The Dwarves in LOTR we’re just ordinary actors who were made to appear smaller with CGI. They were not dwarves in the sense that Peter Dinklage is a dwarf. And yes, we have to use the word “dwarf” here and not “little person”, because there are lots of little persons who aren’t dwarves.(Danny Devito for example.) but anyway, I think that if they just use CGI on ordinary actors for the dwarves in The live action snow white, nobody would say anything. We’ll see I guess. maybe there will be people who will complain that only real dwarves should be allowed to play dwarves, just as only real Asians are allowed to play Asians etc.