It should be closed with further details needed, because it's not a system-agnostic question. System matters for understanding the problem and understanding what solution to apply. Factors that the system influences include but are not limited to:
- What actual qualities do the “exotic” or “normal” races have that would have a player gravitate toward or away from them? In fact, what specifically makes them different at all? We need to consider this stuff if we're going to provide guidance on how to point players in a different direction.
- What kinds of stories is the system interested in telling? How does the choice of race affect the story, or create or resolve problems?
- What does the system offer in terms of incentivisation that the group can utilise? What concrete tools are available for shepherding players and how should they be used?
- In fact, what's the player/GM relationship here, and is there even a GM at all? This changes the power dynamics when making requests of others at the table or when implementing changes—some games vest significant authority in the GM, some vest no special authority at all in them.
These are factors that do not have a “neutral” or “agnostic” answer. Each system (or the lack of a system entirely, maybe it's freeform) has specific answers, where “nothing defined on this topic at all” is also a relevant answer for readers to know.
This means that in different systems, the answers vary a lot.
- In D&D, a group with highly varied races isn't a big issue and solves a lot of problems.
- In a Warhammer game, it creates problems for humans to adventure with non-humans.
- In a World of Darkness game, the answer is digging into splat mixing vs not, and answers about splat mixing tend to be in the vicinity of “yeah, people try that, but it doesn't actually work too well. If you're going to do that, here's how.”
- In Dresden Files, it takes the story in a different direction. There's specific tools the game uses to address fey creatures (narrative permissions related to free will, different fate point allowances) and unique incentives to pick them. It's a significant consideration whether your characters can pass as human; this doesn't matter in D&D.
In lieu of any specific information about the system, people are assuming D&D, assuming its constraints and situations apply, and they're name-dropping DMing and Pathfinder out of an assumption they're relevant. This is pretty fair—it's quite clear the question seems to be addressing D&D, but doesn't want to say so for some reason.
Specifying the system to us is helpful. It gives people knowledge of the tools they can work with, and that's important. Withholding such information and just pretending it's system-agnostic isn't doing anyone any favors. It leaves answerers armed with less knowledge for addressing the problem, and leaves them providing weaker solutions and guidance than they could otherwise speak about. Personally, it seems like a long line of sytem-agnostic-but-actually-D&D questions that assume that the tabletop RPG space is equivalent to D&D and therefore D&D questions can be system agnostic because it's all the same. (We saw this happen a lot during our early years on this site.)
The OP ought to tell us specifically what system or systems they're trying to solve this issue in, rather than beating around the bush. RPG.SE is about solving practical questions based on actual problems that you face, not about generic problems that generically exist out there somewhere. The OP is having this practical problem in a specific system or set of systems, and should tell us what those are.