After Japan lost the war in 1945, the many radio technicians and electronic engineers stationed around the world came back home to Japan. At the time, there wasn't many jobs going round and all most of them could do was to make things like electric rice cookers or pots.
They wanted to contribute to the reconstruction of Japan and called out to all the Japanese engineers to gather at Akihabara. At the time, radio was the only form of enjoyment in an era where printing and other forms of entertainment was scarce - thus the engineers focused their efforts in bringing the people more radios.