Reaching across the aisle has never been more important in American politics. The country is experiencing a downfall that will rival Greece if the parties cannot work together to form some kind of FDR-like plan to help the poor and middle class soon. They absolutely must work together in order to create a prosperous future.
Although bipartisanship is heralded in Washington, it seems like when both parties agree, it screws over the little guy. You see this from monetary policy and foreign policy to the NSA and the PATRIOT act. Although nobody's happy with Clinton vs. Trump, whoever the parties could agree on would be worse because we wouldn't have any choice at all.
The democracy of the United States is based on a system of checks and balances. The two political parties are often at odds on issues, but reach an agreement that takes both sides of the political spectrum into consideration. The two sides hold genuine opposing views. Them coming together to choose a candidate corrupts the process.
The people of the United States deserve to have some kind of choice for a president. If they banded together and nominated the same person for president, there would be not choice whatsoever. If there is not choice than the United States is no longer a democracy at all, but a dictatorship.