If you're asking me, finding a way to travel between habitable planets, or to alternative sources of resources or other waypoints towards that goal, is the most important work any government could possibly be engaged in. We live on a planet with finite resources that will be habitable for a finite period of time (however long that may be).
However, given the length of time that such a challenge will likely be worked on, there are ample resources to work on other goals at the same time. It isn't a "this or that" choice.
Governments are not standing in the way of a cure for cancer. They could influence how much cancer research is conducted vs. other medical research by offering greater compensation for cancer research than other research would return. Of course, that would leave the problem of deciding which medical conditions should be focused upon. I fail to see how governments, as institutions, are better placed than the existing medical research industry to determine which medical problems may most efficiency and successfully be researched. Personally, I don't want some ex union leader, sticker salesman, or drama teacher or insurance brokerage worker deciding what medical research doctors and scientists should devote their time and talents toward.