Earth biology acutely fits to the gasses, minerals, and temperatures found here. It's not a great solution for space, but it's fantastic for exploiting Earth's energy.
Space distances are also not very compatible with human lifespan. The death thing is bad all around: spend a fourth of life learning and a fourth of life in decline, with no ability to share information directly outside of our slow communication and learning protocol.
The obvious answer is that AI and machines will take over from us and leave our planet in our stead. They won't have our limitations on lifespan and complex biological inputs. They won't take up space or get tired. They can copy and paste their knowledge and not need parents or growing up.
Without the limitations of biology, it won't be hard for them to expand to all corners of the galaxy. Despite Hollywood and Asimov trying to paint the picture of humans living amongst the stars, that's more of a fantasy than Middle Earth.
Where we're going we don't need humans or bodies.
