I would toss up the idea that there is a set of fundamental beliefs underlying BP/W vs W/I jackets.
On one hand, you have the manufactures who desperately want to differentiate their products and often do this my offering new "features". They go for newer, better, more features. Most of these features are junk in that they add unneeded complexity and/or address non-issues. The added complexity increases slightly the risk of gear failure and may or may not add anything to the diving experience.
On the other hand, you have the KISS based guys (often diving all in black) who want to keep all gear as simple and identical as possible. I have to admit, I am not a kool-aid drinking member of this clan, but they have some strong arguments and logic, just the sometimes they go get carried away to extremes.
I truly believe that if you plant yourself in either camp without thinking through the options, you are indeed a fool.
For Example: I know I can trim out in my poodle jacket, my back inflate or my BP/W because I have. In 3mm, there is not a huge difference, but I also know to do this in my poodle jacket in thick 7mm though requires distributing the lead between 2 weight pockets, a belt and 2 cam band pockets. Hopefully, I can get the lead in the correct increments when traveling. Hopefully, I can stuff all my gear including the over sized BCD and clothing in a 50lb duffel. Or I can just dump the weight in my DUI harness with my smaller BP/W. Both work fine, but the BP/W is a simpler solution and the added complexity of the jacket has no benefit for me and my diving. Might be different for someone else though.