Some NFTs are stored this way (e.g. Blitmaps, Terraforms, Corruption(*s), &c); it's a more restrictive artistic medium since storage costs are high and technical limits feel like a trip back to the 80s. If you can fit nice art into the constraints then it can become quite popular/valuable since fully on-chain NFTs are actually decentralized (rather than the more common practice of linking to an external image).