Because coal plants cause even more pollution. I'm not sure about vanilla or Warlords, but in BtS having power in a city gives +2 unhealthiness, regardless of which plant you have. I'm not sure if recycling plants affect unheathiness from power or not (the unhealthiness is caused by the power, not the building, even though the power comes from a building, so I'm unsure).
I hear an odd sounding engine, and a FORKLIFT comes out of nowhere and plows my squad down… All I could say was "WTF FORKLIFT?" -bionuke118 on BF2:SF