The true answer doesn't have to be the interesting one, this is basic Design in the Commercial World stuff. If the change in dock connector for the new phone wasn't coupled to restrictions on 3rd party suppliers and an increase in basic costs across the board, including internally at Apple as it has been suffering from labour shortages, partly because of this decision to bring the cables in house, then I wouldn't necessarily put it down to pure profiteering. But from where I am sitting, there is no clear technical advantage to this behaviour, but there is a clear financial one over time.
[edit] Also, if I wanted to predict where this is headed, if all cable production can be brought in house, then why not go the whole hog and chip the cables [edit - I just looked up the spec, given that thunderbolt is an active cable, this has to be the direction they are headed], with some introduced functionality to sweeten the deal on the consumer side and then you can get total lock-in on peripherals, if you like.