Using microwave as method of sterilization provides several advantages:
Steam sterilization method needs very long time and has bad effects on flavor. A succession of rapid heating and rapid cooling prevents significant flavor changes. Microwave energy provides the rapid heat.
Irradiation destroys the molecular structure and generates harmful irradiation residue. Why use a dangerous method if a safer alternative is available. The microwave energy itself is dangerous as it boils water molecules on path. This danger is easily prevented by a suitable enclosure. More important thing, microwave never leaves residues.
Microwave is very convenient to use. Imagine it as a small piece of gadget house in a box.
Reduced cost. Far more lower cost than steam and irradiation methods. The thing it refers to is the time. More jobs could be done with microwave as compared with two other methods.