Why did GE use PCB's?

"PCBs were used as coolants and insulating fluids (dielectric fluids) for transformers and capacitors especially in components of early fluorescent light fittings, the GG1 locomotive's electrical transformers, plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical wiring and electronic components, pesticide extenders, cutting oils, reactive flame retardants, lubricating oils, hydraulic fluids, sealants (for caulking in schools and commercial buildings[6]), adhesives, wood floor finishes (such as Fabulon and other products of Halowax in the U.S.),[6] paints, de-dusting agents, water-proofing compounds, casting agents, vacuum pump fluids, fixatives in microscopy, surgical implants, and in carbonless copy ("NCR") paper.[2]"