Why is a Qigong practitioner not so interested in material things?
Is it because a sacred vow has been taken to renounce worldly things and purely devote one's self to spiritual development?
Worldly things are useful. We use them each day to get things done.
If you practice Qigong though, you may notice that your interest in "stuff" diminishes.
To what degree does it diminish? To the degree that "extra" or "unnecessary" "stuff" fulfills you from the inside.
Why does fulfillment from external things decrease? because internal fulfillment naturally increases with Qigong practice.
How does this happen?
Simply put, we often buy new things or get new things to add change, excitement or fulfillment in our lives. This affects the life inside us. It breathes some fuel into the flames such that they flicker, spark, jump and flare up. But this is only temporary.
The fulfillment that one achieves directly from the inside is more stable. It is about being in touch with the 'life inside'. The very vitality that drives one's actions in the world.
The Qigong practitioner is not trying to get rid of stuff from their life. They are adding life to their life, they are not adding stuff to their life. Naturally, as the life inside expands, the stuff weighing one down from the outside falls off like fruit ripe to leave the tree. It's a natural process because Qigong is about being Natural. Naturally, one feels a sense of ease when this happens.