There is a beauty to a simple, clean design that no amount of detail or crunch can improve. One can go on and on, providing tactical depth but adding nothing. At a point, you are taking away options just to give them back later, and the design becomes "rats in a maze," but the maze here is rules and paragraphs of subclass options. And with every new subclass added, you are taking those abilities away from those who thought they had them.
Oh, I thought as a druid, I was always a bit of a beastmaster. So you are telling me the new beastmaster subclass does that better? Oh, okay, I picked healing. I guess I am a little more inadequate these days. I just will never use my beastmater powers, since they will never be seen as good as the subclass that specializes in it.
In OSE? All druids are druids. If you want to do druid things, just make them up and ask the referee if what you are doing is druid enough. If it is a spell, well, then, it is automatically druid, and what you can do. You don't need subclasses "carving off" things you can't do with each new one added, either because you never knew you could do that and it was just taken away, or "someone else does it better now," and you have the specialization curse.
In the OSR, classes are how we have party specialization, not subclasses. I don't need rules to solve the non-problem that "all fighters are the same," since that's on me to solve. I will do that through my roleplaying, gear choices, social role, and stats. A party of four or five probably will solve the specialization problem through everyone picking a different class, or some using race-as-class to play an elf or a dwarf.
The game isn't giving me rules or subclass choices to make my elf different from other elves; that is on me. This is where my ability to play a character, roleplay, and craft a unique character comes into play. The player skill needed to do this is much higher than 5E.
5E solves the problem by cutting off parts of your class role, forbidding them from other builds, and making you a false specialist instead of a master of all. If I am the druid? I want to be the weather-caller, wild-shaper, druid of growth, beast-master, and harmony priest. I get that in OSE. Thematically, that is much easier for me as a role-player and much better for me to play my class role. I can call myself a "specialist" in one area, but there aren't any rules for that; it is just my choice.
I am likely the party's only druid, so I get to do it all.
Easy. Simple. Clean. Flexible.
We saw the "lie of specialization" begin to seep into the game with AD&D 2nd Edition and the kitbash design introduced in the compendiums. The game began to accumulate the debt of inferior game designers, and it diverged from the original clean, flexible simplicity it captured. 5E enshrines the lie of specialization and writes it into the structure of the game.
Without specialization, my druid is free to embrace all the tropes of being a druid, and I am freer to craft the character I want to play. Nothing is telling me "I can't do that since some other subclass is better than me at it."
D&D doesn't need specialization.
Class choice more than covers it.
D&D is better without specialization.
