The volume of the most compact camera's is NOT constant.
Air presure is not constant.
The space in front of the sensor is air.
(Compact camera's do not have a sealed sensor).

Because of the volume change (zooming etc). the camera is not
airtight, this means air gets sucked in and blown out. While extending
the lens this is going quite rappidly, so there are some 'large' holes in
the camera. When the air get's sucked in, dust get's sucked in as well.

Depending where the camera is kept, there will be dust on the camera.
Keeping the camera in a camerabag which is 'clean' will keep the camera
clean as wel (fairly). Keeping the camera in a dusty surrounding, for
example in your pants or your pockets in your coat then the camera will
get dusty.

Zooming makes that air (and if present) dust get's sucked in.

Sensors in most compact camera's are very difficult to reach even for
professionals and often the operation of removing the dust is so
expensive that the camera is not worth this operation.

So with the camera, you are probably stuck with the dust.

ben brugman.