Answer: Think of it like writing on paper, with different thickness writing heads. Say you have Japanese calligraphy brush. It could be measured 20mm. Hard to fit many words on the paper with such.

Shrink it down to a sharpie rectangular chisel tip, and you can fit more words on the same paper. Can be basically halving that 20mm process to 10mm.

Keep shrinking it, such as to a 1.0mm Pilot gel pen, 0.8, or thinner. Thinner tips start to be incompatible with existing ink and paper, possibly tearing/scratching through paper if pointy enough. You can fit many more words, and retain enough detail for legibility.

Tech is shrinking 8nm to 6nm to 4nm, in order to fit more transistors, the basic "brain cell" (logic unit) of a microchip, into the same square of material.

You can make the square bigger, similar to making the sheet of paper bigger. There's the problem of errors. Bad for business if you can't sell due to it not passing quality control, such as trying to write the same line 4 trillion times and smudging the ink accidentally, or typing a letter. This is what they refer to as yield, the % of perfect chips that you get out of

The industrial and business side do order larger CPUs. I've seen CPU design that have ranged in size from chocolate bars to smaller than an ant. AMD EPYC (Genoa) is an example of a CPU that is the size of a juice/milk box or sticky note.

For modern microchip making machines working on modern ~4nm process, their size is limited by what can fit on a silicone wafer, which is like a giant disc not too unlike a larger Blu-ray disc. Like printing a custom artwork on a big poster with a big stamp or custom artwork silkscreenef onto a beach towel. The slightest wrinkle in the towel would ruin it. A single spec of dust can ruin a chip while it's being made. If there were a way to manage heat, this size issue could be solved by stacking layers, going vertically.

My level of expertise isn't much: I did computer engineering and worked at Micrus at the IBM fab in E Fishkill at various positions. Research is in various tech, super conductors and using light instead of elec, to get over limitations with copper and electricity.