Loss of 3rd party data sales from the tracking embedded in their apps would be my guess.

What happens when you wear one?

How would someone get started doing this?

It’s a flexible coupling for a drive shaft. It probably does show up on stepper motors for 3d printers. It’s used to allow for some misalignment between the motor and the rest of the drive assembly so there isn’t any damage to the motor bearings or binding of the shaft.