Advancements in technology can be detrimental to the environment, lethal, make us dumber, worsen quality of life in several ways, help control and imprison us, and any combination of the previous.
And "expansion into the universe" means little if it's for some lucky few. Why should the rest care, just because if Earth is whiped out those few get to "continue"?
That's even assuming it's doable without something like generation ships - which even at the solar system level is a big if.
https://www.sciencedirect.com/science/article/pii/S016028961...
Increased mental illness might be one, other one is the brain size being limited by the hips of mother. Brains / intelligence also has energy costs which we might not have been able to optimize for yet.
As such, I would say that intelligence is a cost that you run. It allowed for reproduction and survival for humans when they moved towards colder regions for example, but there's little to no reason to maintain that intelligence if you don't need to adapt anymore. I think you need harsh material constraints (I don't know, space faring) to keep it from shaving itself off in order to optimize the human machine.