Here's why:

* Weight vs. Mass: Weight is the force of gravity acting on an object's mass. Mass is the amount of matter in an object.

* Orbiting is Freefall: Astronauts in orbit are constantly falling towards Earth. They're in a state of freefall. However, their horizontal velocity is so high that they constantly miss the Earth as they fall.

* Apparent Weightlessness: The sensation of weightlessness arises because the astronauts and their spacecraft are accelerating together at the same rate due to Earth's gravity. Since they are accelerating together, they don't feel any relative forces, making them feel weightless.

In short, astronauts in orbit still have mass and are still affected by Earth's gravity. Their weightlessness is an apparent condition due to their constant freefall.