If loudness is about pressure, why do tiny earbuds sometimes seem louder than big speakers?

I'm sure I'm missing something basic about sound. I always thought "loud" meant higher pressure waves in the air, so it seems like a big speaker that can move a lot of air should always be louder than a tiny earbud.

But in practice a little earbud can feel painfully loud at what looks like a low volume, while a big speaker across the room can be loud without that same punch. If I pull an earbud out and hold it at arm's length it suddenly seems a lot quieter even though the volume setting hasn't changed.

Is the earbud actually producing more sound pressure, or is it just because it's so close to my eardrum? How does distance factor in when the earbud sits basically inside the ear canal, and does the shape of the canal act like a little amplifier or resonator?

Not looking for medical advice - I'm just curious about the physics. I do some side audio work and listen a lot, so I've been wondering what "volume" really means when comparing earbuds and speakers.