Earbuds often have features like mic beam forming and noise cancellation which require a substantial degree of processing power. It's hardly unjustified compared to your Teams instance making fans spin or Home Assistant bringing down an RPi to its knees.
No doubt, maybe should I have emphasised the "general" part of "general purpose" more. Not a hardware person myself, I wonder whether there would be purpose-built hardware that could do the same more cheaply – think F(P)GA.
These sorts of things feel like they would be quite inefficient on a general-purpose CPU so you would want to do them on some sort of dedicated DSP hardware instead. So I would expect an earbud to use some sort of specialized microcontroller with a slow-ish CPU core but extra peripherals to do all the signal processing and bluetooth-related stuff.