The memory limitations that you cite, as well as the driving problem behind slow updates, can be squarely put at the feet of Intel. They have pushed back meaningful updates for a couple of years now. I am not implying that they are doing so deliberately, but rather have been unable to make meaningful upgrades.
To take the memory size limitation, that is because Kaby Lake processors are the only ones to support 64GiB, and the models that Apple would have used were not available (let alone in Apple quantities) until long after the current MacBook Pros shipped. And I think you are a bit mislead about "battery issues". For most workloads Apple's newest MacBook Pro's have 10+ hour battery life. The only place where it is not better than the previous generation is on the 15 inch models on workloads that cause the GPU to kick in. There the battery simply is not enough to really feed that power-hungry GPU. This was an engineering decision (tradeoffs between a better GPU, thinness, and battery life for certain workloads), and real deserves a more thorough understanding than your summary indicates.
A similar conversation applies on the MacPro front. Again, the Xeon processors that Apple used have not been upgraded in a way that justified updates. I wish that Apple had released speed-bumps along the way (and adjusted the bottom-end price along the way), but there was really not enough change since their release to justify a re-work since then. A GPU update might have been nice, but (full disclosure: I worked at Apple, and helped test one aspect of the GPUs) Apple spent a lot of engineer time making those custom GPUs sing on the workloads they were for: FinalCut Pro (not gaming). Likely someone crunched the numbers on sales and determined that it was not worth the expenditure to do that again for a mid-term product. Whenever it is updated again we will see if Apple goes the custom route again.
I also don't think you are evaluating Apple chip work nearly well enough. I you look at the CPU/GPU work they have done on the iOS devices; for the last 4 or so years competitors have been at least a year behind on most real-work testing metrics. Only in multi-threaded tests does anyone else remain competitive within a year timeframe. That is despite Apple being lower-power and lower clock-speed in almost all cases. And the delta has been widening as Apple ramps up on this. They started with nearly off-the-shelf processors, but are now on their fifth version of increasingly modified ARM ISA (Swift, Cyclone, Typhoon, Twister, and now Hurricane), each of which had increasingly custom versions of the paired PowerVR GPUs.
None of that work is about lowering costs, all of it is about improving performance. If Apple only wanted to lower costs they would be using Samsung or Qualcomm licensed CPU designs.