Pray tell, how do you think "they" should optimize game assets? People who have zero experience in game development love to talk about "optimization" like it's a slider in the options or some challenge that can be solved by throwing resources at it. Modern compression algorithms like Oodle are about as performant and artifact-free as mathematically possible. Everything beyond that is a trade-off between quality, size, and performance.

But are you thinking about it in abstract? Would you prefer a game to have occasional pop-in, stutter issues, and CPU spikes in exchange for a smaller size?

(edit) Before you say it, I know there are relatively low-fidelity games that run like ass. Those are usually caused by poorly written game logic or shader codes, which can be refactored, but won't have an effect on file sizes.