I think ever since the Yuan-ti Pureblood got released as a PC option in Volo's, they've been like SUPER cautious about giving playable races that straight up have an immunity to damage types.
I mean, look HOW LONG it took them to FINALLY give us Force, Necrotic, Thunder, and Radiant as damage type choices that a Dragonborn could use for their breath weapons? Because anytime a similar choice of damage type selection for an ability or what not was an option, WoTC ALWAYS gives the standard Fire, Ice, Acid, Poison, and Lightning selection choice. The Gem Dragonborn have been the ONLY exception to that paradigm so far IIRC.
WoTC just seems to be TOO cautious at times. Despite allowing various options before in the past that was a bit of a bump in power on the PCs end.
Yeah, I mean, imagine you had resistance to force. How often is that going to come up? What does it break? Not a gosh-darned thing. Bear Totem Barbarians can take half damage from force during major confrontations, almost effectively doubling their hit point total (save for psychic damage), and that's perfectly fine. Sure, some damage types are common- undead have a tendency to throw around necrotic damage, fire-using creatures are a dime a dozen in D&D. In a lot of cases, however, it's a situational ability, depending on the campaign and foes fought, it could be little more than a ribbon.
Like being a Ranger who has practiced fighting Giants. Sure, Ogres, Trolls, and the like aren't exactly uncommon foes, and if you're playing Against the Giants or Storm King's Thunder, it will be handy to have bonuses against Giants- but even there, these are not the only things you fight.
When I played SKT, the most memorable fights were against a remorhaz, a dragon, and a kraken. Giant-slaying would not have helped.
But I get it. It isn't that WotC doesn't realize these things. They're probably tired of the knee-jerk rage from DM's who imagine the worst-case scenario, that a player could manage to trivialize one enemy type or encounter, perhaps even one of their favorites.
The tired old "5e is easy mode" arguments come out, and the wail about how "power creep" is destroying their ability to challenge the players. Which, you know, maybe a new DM might run into some issues, but it doesn't take a lot to trivialize an immunity or resistance. In fact, it's so easy to do, that it's harder to give the player moments where they can shine.
What a lot of people seem to forget, with these sorts of arguments, is that 5e's model isn't based on attrition the same way older versions of the game were. The players are generally supposed to win in 5e. It's possible to lose, but the circumstances that cause this to happen are extreme, by design.
WotC wants to make money, and they feel the best way to do that is not produce a game with Dark Souls-esque difficulty. If Billy the Noob sits down to play D&D, if his first encounter results in his character dying to a goblin's spear, he might decide this game isn't for him.
Now, that having been said, a DM can certainly house rule the game to be more difficult. Gritty realism, less generous resting, banning elements they think make the game too soft. And that's fine! It's all about what your playgroup finds fun.
But the instant WotC produces anything cool for players, why, it's the death of the game! And rather than just quietly saying "I think it's a bit much for my campaign, but I'm sure it's fine for others", you get "TWILIGHT CLERK HAX!!!!1111", and endless threads talking about how this thing or that thing is destroying their vision of the game, which most likely was already not the default anyways.
And I'm not defending WotC here, mind. Some things they make are a bit extra. Just as some things that they make are too conservative, to the point that no one is excited to use these options.
What truly bothers me is, I don't understand why WotC chooses to listen to this feedback sometimes, and ignore it completely in other times. They went ahead full steam with the Tasha's Cleric archetypes, but nerfed the thing about Yuan-Ti and Kender that made them unique. It's truly maddening.