Why ceramic IC packaging?
In IC packages it certainly is desirable to dissipate heat with the lowest possible thermal resistance. 

However, at the same time, electrical insulation and protection from oxidation / corrosion are also desirable, at least for discrete components that are likely to be handled or exposed to the environment.

An insulating packaging such as ceramic or plastic allows this insulation and protection, while permitting heat dissipation through controlled paths, such as integrated heat sinks or heat sink tabs in some packages, or just through the pins in others. 

Many IC packages are also sold as bare die, or wafer level chip scale (WLCSP) packages, for the circuit assembly process to directly connect to the PCB. The bare chip is then environmentally protected using epoxy potting or similar protection coatings, after soldering or bonding of the lead bumps to the circuit board.

Such bare packaging of course requires more sophisticated assembly equipment than the much larger IC (and larger contact pitch) packages do, so they aren't for everyone.