In an elected system, the representatives are to a degree self-selecting for their enthusiasm for the job. Under a system of pure, universal sortition the individuals are not chosen for their enthusiasm.  Many electoral systems assign to those chosen a role as representing their constituents; a complex job with a significant workload. Elected representative choose to accept any additional workload; voters can also choose those representatives most willing to accept the burden involved in being a representative. Individuals chosen at random from a comprehensive pool of citizens have no particular enthusiasm for their role and therefore may not make good advocates for a constituency.