Because Earth is a sphere moving around the Sun, we can easily see the Milky Way’s center only in certain months. In other months, the Milky Way will be too close to the Sun in the sky, where sunlight will overwhelm and obscure it from view.
Flat-Earthers claim that the Milky Way is visible every night “proves” a flat Earth. In reality, we are inside the Milky Way, and some parts will be visible. However, a specific part of it, like its brighter center, will not be visible every night.