Whether at a sum that decision was lucrative or not is inconsequential, as that comes down to how the market responds to their decision, but what you can argue is whether they make more off headsets now than before.
Before they bundled regular corded buds, and you purchased new ones when your old ones broke. Now they sell $180 USD AirPods, and Beats, and bundle (IMO) clunky adapters. While I don't have data on this, I'm fairly confident in assuming their decision was made on this basis. The question is if this turned out as they hoped in sales.
> The simpler explanation in my mind is that Apple wanted a thinner phone, and they did what they needed.
How so, when there was obviously space enough for an end-user to fit a jack inside the final product?