I believe the suggestion about immersion is that it wouldn't make sense to introduce exotic races just for PCs.
If that is true ...
Then i purely disagree.
This game dont cover even 1% of Faerun ...
Therefore opposite is corect, for rare races, it makes perfect sense to not meet any NPC of same race as our Tav will be.
Quite honestly (and feel free to corect me if im wrong) i cant help the feeling that even Dragonborn are quite rare in the City of Baldur's Gate!
As far as i know, they tend to live a little more North/East ... and also quite far from this particular place.
So, personaly i expect at best up to 10NPCs of this race.
Or our PC is the only example of their race so players who choose not to play that race aren't bothered by it, but then we need character models and animation that will be used only for the PC which doesn't seem very efficient.
Question is if efficiency is even concidered.
Personaly i dont see much reason even in giving Elves their own animations.
And yet ... they have them.
Also, some recyclation is allways possible imho.
If you want Warforged to move like a construct ... well, we have Bernard (and constructs in city, im no animator, but i believe they should be able to just scale it down) ...
If you want Lizardfolk to move like a reptile ... well, there are Dragonborn ...
Not really sure about Tabaxi ... but arent there some spells that allow caster to grow claws? I only remember one Druid cantrip, but that was not from PHB.
Baldur's Gate literally has a dedicated ward for exotic races and cultures, Sow's Foot.
Don't forget none of the game takes place in a back water region of Faerun, its set so far in Baldur's Gate which got an influx of immigrates of all kinds during the Spellplague and gets trade from across Faerun and beyond, or along the river that is a major trade route.
And just exploring the races that we know had a race tag at least at some point & Goliaths.
And compared to humans, elves, halflings, and dwarves, Dragonborn are rare, but not so rare that folks don't see them now and again. In the setting as a whole Dragomborn aren't rare at all, because they are common on Abeir and places transplanted from Abeir to Faerun.
Other rare races will vary more on how common they are, Tabaxi in large numbers are immigrating to Faerun for various reasons. Tritons have a host of cities in both Oceans and Seas, Genasi not only have a large population in Calishan, but great numbers ended up on Faerun from Abeir (and others came from the elemental planes directly, or desend from Genies), Drow have gotten better PR rescently and have the largest population on Toril, except maybe Sea Elves, Lizardfolk were rare outside of swamps, but many got driven out and neede somewhere to go, not sure how common Kenku are, Aacrokra have their own cities in places like Chult, Tortles are super rare outside of Chult, but are too adorable to fear, Firbolgs are rare, but not not so rare as to freak people out, Goliaths will need a massive FR lore update in 2024, Aasimar & Tieflings are common in the old empires region.
The two odd races that would be rare even among rare races are the Githyanki, who while having a nearby creche are not that normally socialable with out races, and have super small numbers on Toril under normal circumstances, they only come to Toril normally to raid and reproduce, but given Dragon riding Gith have been saving folks from Mindflayer Nautiliods, folks may find they like the Githyanki alot more.
And the other race would be Warforged, which comes from Eberron, a world most on Toril have never heard of, but folks have seen or heard of enough magical contructs that as long as they don't act threatening, they won't be a big deal.
