Shouldn’t immortality lead to a static culture, as older people tend to be more conservative?

That’s because human brains become less plastic as they get older, and people who find it more difficult to learn new things generally prefer to avoid having to learn new things.

Exactly why do you think that this particular side-effect of bioentropy would be exempted from the general cure?

I would argue that (in humans, at least), the desire for a static environment is a part of our evolution from Mk 1 Plains Apes, where disruption in the environment meant we’re gonna starve by tomorrow night. If something is changing, it means that it’s a disruption, and the monster of hunger looms with the next sunset.

The Eldrae, on the other hand, have everything in their biology and culture engineered so there is no stability, no static culture or static place to live. Even the basic wage and material structure requires a citizen-shareholder to maintain a certain level of reputation and that means dealing with sophs, which requires you to not be static. Even the Eldrae cultural goal of getting access to the root command structure of the universe and making it perfectly just and fair means that there is no lesser goal to settle for.