Because you have to park it 900AU away from the sun (Voyager 1 is at 147AU after 40 years and not in a solar orbit) and it has to have a special kind of coronagraph that flies as a separate spacecraft from the telescope (hasn't been invented yet) and your telescope is limited to looking at objects directly opposite the star from the orbit of the spacecraft. At 900AU it would take decades to slew such a telescope to view a new object in the sky.
At the current time this is basically a science fiction project that promises that if we put a very special spacecraft in a very specific place then it is within our technological capability to image an exoplanet. That doesn't mean it's even a remotely practical idea. It's interesting to talk about but useless to get all worked up about why it's not getting funded.