You might not have, but the language in Volo's is basically identical to that of ultra-racist textbooks from the 20th century (a toned down versions existed into the 21st), and if you are unfortunate enough you can still see Facebook posts and the like promoting the same ideas - sometimes the focus changes (i.e. which exact race), but the vile ideas stay consistent. Maybe imagine being a black person and aware of that, perhaps having been subjected to that kind of racism, and reading Volo's, and seeing that Orcs are being characterised in exactly the terms your ethnicity has been, and the game is saying this is real and true (in the game) and they're chaotic evil and so on. At best that's going to make someone feel pretty uncomfortable, I'd suggest.
If you're white, and especially if you're actually not familiar with the sort of incredibly sick racist stuff people come out with, it's probably easy to miss this. Indeed, one suspects that's what happened with Volo's - the writer probably didn't even think "Hey isn't that what they used to say about black people?!" - because he was white and had never had to think about racism beyond "It's bad, don't do it" and simple stuff like "cops are much more unpleasant to black people". But this is the really hardcore kind of racism, that unless you're subjected to this kind of racism (as many non-white people are, sooner or later) or interested in racism as an issue (rather than simply something that you're against), or a well, yes, a bigot, then you might not be familiar with it.
That you assumed it's "overblown" is a bit sad but perhaps it was poorly explained previously.