[CDSlice]

The problem is we can't launch another Voyager mission. The Voyagers took advantage of the planets being aligned in just the right way to allow them slingshot through the outer solar system. This won't happen again for another 100 years or so.

Now we could design probes that are just for going into interstellar space but it would be a hard sell when you are competing against missions like sending a drone to Titan. Even the New Horizons mission to Pluto barely made it through NASA's project selection process and IMO expanding our knowledge of Pluto is more valuable (and sellable to the public) than a mission to literally nothing.