system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the physical size of computer parts in desktops stay roughly the same?

So I've been building my own pc's since around the late 90s. Since then we've had single cores, dual cores, quad cores, 6 cores and now 8 cores each with varying transistor densities. Why has the actual physical size (the piece of metal you hold in your hand) roughly stayed the same (2cm-2.5cm^2). Why did we land on that size in the first place?

Even in servers I've seen, they are around the physical size of a desktop cpu just with multiple on one board. Is there a reason they don't make for example, a 10cm^2 cpu and cram like 16 cores into it instead of 4 quad core cpus?

RAM has also stayed roughly the same size.

TL;DR: What is determining the physical size of computer parts.
gpt
Firstly, there's the fact that there are standards according to which your computer parts are built (see, for instance, ATX). Diverging from those is a very big deal, and incurs massive costs. Processors don't directly fit in those standards, and their slots change every few months (usually with pin count) - i'm sure you've experienced some amount of discontent when you've had to upgrade a m/b together with a CPU.

Secondly, there's the problem of heat dissipation. Assuming constant physical dimensions of, for instance a CPU, the amount of heat it emits will be greater as its fabrication process gets better (i.e. more transistors & memory fit in the same space). _EDIT_: Although this is a general rule of thumb, it might not always apply; some newer processors, for instance, are clocked at a lower frequency while packing more cores than their predecessors, leading to less heat emissions. At any rate, the greater dimensions allow for better heat dissipation through cooling fans, liquid, and so forth.

Thirdly, we've only recently had a serious incentive for reducing physical size of components, namely _smartphones_. As you can see, engineers have been very successful in tackling that issue, but this comes with certain tradeoffs (battery life, limited processing capacity, etc).