I imagine it’s far more economical to have one foundry that can make a general purpose chip that’s overpowered for 95% of uses than to try to make a ton of different chips. It speaks to how a lot of the actual cost is the manufacturing and R&D.

The only real problem I could see is if the general purpose microcontroller is significantly more power-hungry than a specialized chip, impacting the battery life of the earbuds.

On every other axis, though, it's likely a very clear win: reusable chips means cheaper units, which often translates into real resource savings (in the extreme case, it may save an entire additional factory for the custom chips, saving untold energy and effort.)