Yes, but it seems to me the solution to that is world building: show me a world where goblinoid cultures are diverse and fully developed. I think setting books are a better place for that kind of information. It does pose a problem of how to describe a goblin in the core MM though. 5e monster books might be the worst of both: bloated descriptions that still manage to paint entire races with a broad brush, to the point that removing text actually helps make creatures more varied.
So, D&D's problem here is the fact it isn't developed for one setting, but multiple ones.
Star Trek, for the most part, has one general overall setting and timeline (with some divergence, notably the Kelvin timeline). A species like the Ferengi or Klingons have had decades of writers writing about the same group of people, adding, and remixing as needed, until something closer to a fleshed-out culture emerged. You could say the same is true of Pathfinder which has used the same setting (Golarion) for all supplements and adventures. Barring the things retconned out or never-spoken-of, every bit of Pathfinder lore expands Golarion and refines it.
D&D has never had a single setting. Well, one that stuck, I guess. It had a few default settings, but it always immediately tried to support multiple settings at once. The closest we got to this might have been the Nerath/Nentir Vale era in 4e and early attempts to make Faerun the sample setting in 5e, but both times people clamored for more settings.
This paints a problem as in Pathfinder there is one race of elves that can expanded upon supplement after supplement, but in D&D there are Oerth elves, Faerun elves, Krynn elves, Eberron elves, Ravenloft elves, Mystara elves, Athas elves, etc. Each a little different than the next, and in some cases (Eberron and Athas) radically different. Now, imagine a setting book that tries to create a fleshed-out culture for that setting's elves, dwarves, dragonborn, orcs, goblins, dragons, beholders, giants, etc. You'd fill 400+ tomes just doing that! And most settings don't get support beyond one book, so you'd either end up with a bunch of creatures that have one paragraph culture (defeating the purpose) or are just ignored. D&D lore is not additive, its competitive.
D&D has tried to skirt the issue with a "default + exceptions" system: the Core books provide a default or stock version of creature in question, and when a setting diverges from it, it spells out the difference. Except now, we are leaning towards no default, just blank slates that settings will have to address in the limited page-count they already have. I don't see how any cultural detail gets fleshed out in this model, and instead we are going to get very generic descriptions and stat-blocks with limited information.
OF COURSE, if D&D wanted to abandon the multiverse and create a unified D&D setting akin to Golarion (Nentir Vale 2.0) and use the space in the PHB, MM, supplements, and modules to explore various aspects of the setting in great detail, the work would be much simpler. Volo's guide goes over the different types and tribes of orcs in Nerath 2, Fizban's guide goes over the dragons and dragonborn cultures of one setting with great detail rather than try to adapt to a dozen different worlds, you could do it. Of course, no setting right now is in a good place to become the default setting (most 2e era settings are carrying baggage issues, and Eberron is a little too unique to be D&D's default setting unless you want dragonmarks and warforged as core).
So, as I see it, there are two choices effectively if the current model is no longer working.
1.) Create an all-encompassing monosetting that D&D can expand in great detail, while leaving ALL other settings in the dustbin.
2.) Make the core rules extremely vague and generic and assume that the DM will have to do all the major lifting using some guidance from various setting books.
To be honest, I'm not a fan of either. But this is the Sophie's Choice that we're facing. What's more important: multiple diverse settings or multiple diverse cultures per species?