Why do many surrounding school districts not give periodic raise

Green Creek - Why do many surrounding school districts not give periodic raises to their substitute workforce? This seems to be a common theme; hard working and dedication mean nothing to the administration. I personally know from experience from working in this area of not getting a pay increase in over many years. It is an insult to expect a sub to carry the same workload as their contracted employees, for the measly hourly rate received and no benefit package.