Because it shows that with constant optimization pressure from natural selection and no intelligent insight, there were no diminishing returns to a search for better brain designs up to at least the human level. There were probably accelerating returns (with a low acceleration factor). There are no visible speedbumps, so far as I know.

Were the brain designs better because they were more powerful or more intelligent?

That is how many of the improvements were adding more resources to the brain (because they paid off in this evolutionary case), rather than adding more efficient programs/systems.