My understanding is Robespierre considered private property a concern that took a back seat to the individual right to life and sustenance. Why wouldn't he be a natural ally to the various Enragés factions demanding price controls for bread? Why wouldn't he consider priest and radical agitator Jacques Roux an admirable Republican for his dedication to the poor?
While we could classify the Jacobins, Montagnards, and Cordeliers as "leftist" in today's terminology, the reality is that there was intense conflict among those groups to legitimize their vision of the Revolution. After the execution of Louis, these were rivals, not like-minded groups working towards a common vision. The Mountain rode a tidal wave of popular sentiment to defeat the Girondists, but it's impossible to get that genie back in the bottle. A constant state of revolution requires a constant supply of counter-revolutionary enemies to sate its hunger, and with the Girondists removed, it was incumbent upon everyone to find (and point out) the next-least-radical amongst them.
On 25 June 1793, Roux denounced the Jacobins, who he had just supported in their fight against the Girondins a few weeks prior, for not going far enough by outlawing speculation and hoarding. The narrative of betraying the Revolution through half-measures is a common theme during this period. Robespierre, of course, responded to this attack with an attack of his own, tying Roux to France's foreign enemies.
On July 4 (and I'm skipping some things--events moved very quickly in Revolutionary France), Marat attacked Roux's character in Publiciste, further isolating Roux's influence and access. This lead to further accusations and a trial.
Slavan, Morris. "Jacques Roux: A Victim of Vilification." French Historical Studies 3, no. 4 (1964), 525-537.
Hanson, Paul. The Jacobin Republic Under Fire