Why are incinerators the most expensive form of waste disposal?
Combustion reactors are difficult to operate.
The equipment needed, the contamination control mechanisms installed, the transport of waste to the incinerator, etc. are all expensive. You need to control gases and particles that are emitted from the smokestack of such places. Moreover, there is always an unburnt material that is left behind. This material (ash) could be hazardous. Therefore, you have to manage it properly.
Damages to the public health or environment is another issue. You should best manage workers' health.