In the Clone Wars we see that the separatist use mostly droids in their army. In some instances we see some people fight alongside the separatists, inflicting serious damage on the republic army, one such example is the battle(s) on geonosis.
The droids are a cheap and efficient force to field, but they have shown some weakness in combat with clones.
Therefore, why are they not drawing more troops from their liberated world(s)? Especially later in the war when stronger droids were too expensive to manufacture. Doing this would have bolstered the separatist army on the battlefield.
PS: I guess the question can be asked of the clone army too. Why utilise a predominantly clone army rather than using the huge population of the republic.