Current political mores have certainly tried to make all the races into humans but I think that the Tolkien races can be made to be as common or exotic as you like.
Ever since 3e I've found that the number of races ginned and made playable to be more problematic than anything, Tieflings are a good example, it used to be a template you'd add to an existing race, but I think for external reasons their popularity took over and now they're their own race. Now repeat that process a dozen of times for every interesting looking monster-race and exceptional extraplanar idea and I feel like it begins to unsettle the narrative, a lot like how comics books progressed from stories about fighting crime to stories about collapsing multi-verses into themselves to stop existence from ending....
It isn't a "political more" that people want to play something exotic or unique. Monster races being playable is a time honored tradition in DnD going all the way back to 2nd edition (1st if you count half-orcs who fill the same niche) because, surprisingly, different people have different tastes and preferences. Not everyone wants to be a human, pointy eared human, short human, shorter human, or even shorter human. Lots of people also love the look and lore of a beefy orcish warrior or a cunning and vicious lizardfolk.
The Forgotten Realms is, above all else, a setting designed to accommodate as many character ideas and stories as it can possibly contain. Always has been. But as times evolve and more people come to the table and ask "Hey, can I play this?" the setting itself also evolves so that it can reply "Yes" because that is the nature of DnD and Forgotten Realms. To be accommodating to the wants and needs of as wide a range of players as possible so that everyone at the table is having fun.
And, of course, to get people to buy the books and make Wizards money.
