mpc755

Dark matter fills 'empty' space, strongly interacts with visible matter and is displaced by visible matter.

The reason for the 'missing dark matter' is that the galaxy is so diffuse that it doesn't displace the dark matter outward and away from the galaxy to the degree that the dark matter is able to push back and cause the stars far away from the galactic center to speed up.

It's not that there is no dark matter connected to and neighboring the visible matter. It's that the galaxy is not well defined enough to displace the dark matter to such an extent that it forms a 'halo' around the galaxy. Without the dark matter being displaced to the extent that it forms a halo, there is no lensing of the light that passes by the galaxy.

A galaxy's halo is not a clump of dark matter traveling with the galaxy. A galaxy's halo is the state of displacement of the dark matter.