[W98] Winterhalder, Bruce, "Intra-Group Resource Transfers: Comparative Evidence, Models, and Implications for Human Evolution", http://www.unc.edu/depts/ecology/winterweb/intra_group.html 

The reason for cartels failing comes down to the simple incentivisation of the most efficient member. The strongest cartel member always ends up propping up the weakest. This leads to a strategy of defection