It's just a tactic to get a higher average price while being able to advertise a lower price. What makes it infuriating is memory is dirt cheap. That extra 8GB probably costs them $10 at most, but would add to utility and longevity of their hardware quite a bit.
They are supposed to be "green" but they encourage obsolescence.
They align need with more CPU and margin. Apple wants as few SKUs as possible and as much margin as possible.
8GB is fine for most use cases. Part of my gig is managing a huge global enterprise with six figures of devices. Metrics demonstrate that the lower quartile is ok with 8GB, even now. Those devices are being retired as part of the normal lifecycle with 16GB, which is better.
Laptops are 2-6 year devices. Higher end devices always get replaced sooner - you buy a high end device because the productivity is worth spending $. Low end tend to live longer.
People looking for low prices buy PC, they don't even consider Mac. Then they can have a computer with all the "higher numbers", which is more important than getting stuff done.
They are supposed to be "green" but they encourage obsolescence.