The only reason we need dark matter to exist is to explain the things we can see. For galaxies to work they way they work, given current understanding of how gravity works, they need more mass. That mass has to be somewhere in the galaxy. And there are plenty, as in trillions, of galaxies that are entirely contained in what we call the observable universe.

Because the gravitational effects of dark matter can be seen more locally.

For example, the rotational velocities of stars within spinning galaxies don't match the gravitational force that should be generated by the visible matter within those galaxies. To produce those velocities there must be a lot of unseen mass within those galaxies. Mass that is beyond the visible universe wouldn't increase the centripetal force within those galaxies.

Similarly we need unseen mass to account for the amount of curvature that we observe in instances of gravitational lensing. Such mass would need to be between us and the light sources, not beyond those light sources.

The matter that is missing is in the part of the universe we can see because we see it's gravity.

Because we can see tens of light years in every direction. And the matter we see doesn't match with our observations.