Without counting compression, graphics size goes up on the square of the resolution. You have a 10×10 image, that is 100 pixels you have to save. You have a 20×20 image that is 400 pixels. Back in the 90s, I had an 800×600 monitor: 480,000 pixels. Today I have a 1920×1200 monitor: 2,304,000 pixels. So every image you make is going to take a LOT more space. Plus, you have to make a lot more of them, as you have to texture every part of a 3D model.
Now, compression technology has gotten a LOT better, which helps. There have also been some amazing work done in generating graphics through algorithms, check out https://en.wikipedia.org/wiki/.kkrieger but so far hard disk space is cheap.