We still do optimize software today, it's just that there's a cap to how much computing you can really need for stuff like flying through space.

The most impressive optimized software things we do now tends towards the more abstract, or banal in modern views.
Calculating the most efficient route to launch a spacecraft to slingshot off a bunch of different planets takes more computation than actually flying or controlling the spacecraft.
We can also model every particle involved in a nuclear detonation to optimize blast yields, which is how we optimize lethality while reducing the number of warheads.
Video games are also typically pretty optimized at their core, it just tends to be overshadowed by being "boring" uses.