Earlier quoted context omitted.
They were removed only when few people used them because there was a better alternative. Many, many people use headphones with 3,5 mm plugs and it is not at all clear that the alternative is better.
Well it is pretty clear that the alternative is at least satisfactory. Because iPhone sales aren't dropping because of the headphone jack and people seem to be enjoying Bluetooth headphones given how popular those are.
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.