I think this really is why you are having such a hard time here. You aren't used to engaging in fiction, so the ideas common in fiction seem much stranger to you than to us.
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Sure, but most DMs have Lizardfolk in their game worlds already. They are just generally atangonists instead of PC options. Same with Orcs, Goblins, Hobgoblins, Bugbears, Yuan-Ti, and Kobolds.
The biggest difference is taking those races from "always the enemy, kill on sight" to something that could be talked to, reasoned with and traded with. And considering how often in human history vicious enemies also had trade relations because they were next door neighbors? Not outside the scope of reason.
I mean, take the MM, and find every single creature with an intelligence higher than 5. Even if you take out the Undead, the extraplanar creatures, and the constructs, you have a lot of sentient beings running around your world doing things.
So, the problem never seems to be "we have too many sentient beings in the world" but is instead "we have too many beings let into the towns and cities of the world instead of being antagonists out in the wilds"