I think you’re reading “exclude” and considering “include” as pertaining to evidence in the passage, rather than “the possibility.” Think of “exclude” as synonymous with “rule out.”
The flaw in the passage is that the author has just jumped on one possibility, with tunnel vision. Is it possible that they’re motivated by snobbery? Sure. Are they’re other, legitimate possibilities? Again, Sure. And the problem with the argument is that it doesn’t *exclude* (rule out) those possibilities.