Re: Point
Honestly? I think it's at least partially about the physical dimensions of the chip. The extra 8 efficiency cores take up considerably less space on the die than the power cores. The new chips are the same width but longer. For Intel to provide 16 power cores, the chip would be considerably larger.
For ATX motherboards that isn't an issue, probably not for mATX either but if you're trying to build an ITX system, Threadripper sized chips start becoming decidedly inconvenient.