Why all image/video models are so oversized?

I am playing with different models for some time and I realized that there is no practical difference between official versions of models like Flux Fill / Flux 2 Klein, Qwen Image Edit, Wan VACE... and their quantized / fp8 / nunchaku'ed versions

So what is the point of not providing smaller optimized versions of models by authors?

From what i understand if weights are not open sourced then the community cannot train custom versions so providers could do this instead but they dont