Why did the sans-culottes and the jacobins cooperate at first why did that cooperation end?

The Jacobins and the sans-culottes cooperated at first because they wanted to overthrow the current monarchy. These extreme Jacobins were called the Mountain because they were seated way up the Assembly Hall. They were more cooperative than the Girondists were.  

The cooperation ended when Maximilien de Robespierre and his now dominant Jacobin Club turned against the radical factions of the National Convention, including the sans-culottes, despite them having previously been the strongest supporters of the revolution and its government.