Bluetooth was a step sideways. I like not having my cable get stuck under my chair wheels but holy fuck its annoying to use when you have multiple devices.
When you buy into Apple you are supposed to follow the trend. It has been the case since the earliest Macs. So it is not surprising that Apple followers simply do what Apple tells them to do and switch to wireless.
I don't like it but it has value. Apple products tend to work quite well when used as intended.
As for sales dropping, smartphone sales do drop. Or at least, the upgrade cycles are becoming longer. It is mostly because phones are becoming "good enough" for many years, but the removal of the headphone jack may have played a tiny part.
Because iPhone sales aren't dropping because of the headphone jack and people seem to be enjoying Bluetooth headphones given how popular those are.