Throughout the 90s and into the early 00s, we relied on the standard beige mid-tower PC case. There was only really one color and design.

1) Lack of any ventilation

Old tower desktop PC cases had perhaps one chassis fan on the rear, requiring the loud jet fan to handle all airflow management through the entire case.

This was acceptable back then since components didn't produce too much heat, but installing even a baseline Core Ultra 5 or Ryzen 5 processor and a discrete GPU will send temperatures into the stratosphere, unlocking the thermal throttling award.

They simply didn't have enough ventilation for use with today's components, something we still complain about with some PC cases.

2) Too few fan mounts

And because we had very little in terms of ventilation, there wasn't a need to have more than one or two fans inside the PC. This is no longer the case (pun intended) and you can comfortably install up to 9 fans (if not more) inside more affordable cases.

The more fans installed, the more airflow you'll have and the slower they can spin resulting in less noise.

3) Awful front-facing I/O

Modern PC cases will have an audio jack and a few high-speed USB ports. If you were lucky to have front I/O in the old days, it would be limited to slow speeds unless you're comfortable replacing the ports with new ones.

The number of ports available is also limited and USB-C wasn't even thought about in the 90s. 

4) Massive HDD and disc drive bays

You'll still find hard drive cages inside many mid-tower and full-tower cases today but these are often removable, freeing up the space for other PC parts if needed.

Old PC towers had fixed cages that were part of the structure. You couldn't remove them (easily) and had to deal with more bays than you knew what to do with.

5) Incompatibility with today's GPUs

I don't think you could fit an RTX 4090 or RX 7900 XTX inside any old PC cases. They simply weren't designed for enlarged expansion cards. Discrete GPUs were still in their infancy in the early 00s and many of them were single-slot affairs.

There was also less cabling to deal with since many of them only needed power through the PCI (or AGP) slot

6) A design sent to the dustbin of history

Like anything in life, trends change. You can analyze a photograph captured in the 80s for hours wondering why we moved on from neon lights and funky hairstyles, but I doubt most of us would want to return to that period for absolutely everything. 

Source - XDA 

Signing off

@Rahul S 

@iQOO Connect @NITIN @Aojesh @parakram_h