It is likely that those Netanyahu supporters who despise Lieberman, or those Lieberman supporters who look down on Netanyahu, will have a very hard time voting for a joint ticket.
Question: Suppose that the Likud and Hadash parties decide to run on a joint ticket in the upcoming elections. How many votes would they get? The answer: Most likely zero. Why? Because there is not even a single person who simultaneously supports both Likud and Hadash.