Because the Japanese pronunciation of Kudo Shinichi is Kudou Shinichi, which is very similar to a drum washing machine. This name is different from Conan's other nicknames and has nothing to do with the plot. There is only one truth, and that is that the Japanese name of Conan's original body "Kudo Shinichi" is "くどう しんいち". The Japanese pronunciation is "gong tong xi yi qi", which sounds very much like a "drum washing machine" to Chinese people. Many people have simplified his surname "Kudo" and only call his original name "Shinichi" as "Washing Machine".
Except for Kudo Shinichi, the pronunciation of "Edogawa Conan" is very similar to "show me your ears", and Maorilan is "Magic Orchid" (this is very appropriate, Xiaolan is indeed very (has magic power), and Mouri Kogoro is even better. The pronunciation is a bit like "magic is so magical". It seems that dad's magic power is even better.
Extended information
As a mystery animation, "Conan" can be said to be very popular. As we all know, Conan's original name was Kudo Shinichi, because of a certain Once the villain's conspiracy was discovered. So he was fed poison, but the poison did not kill him, but made him smaller, so he was named Conan.
After Shinichi became smaller, no one knew his identity. However, although his body became smaller, his IQ did not change, so he could still solve crimes. However, this Shinichi was... The majority of comic fans have nicknamed it "Rolling Washing Machine".
Baidu Encyclopedia—Detective Conan