Why Cilantro Tastes Like Soap
Quoting The New York Times:
Flavor chemists have found that cilantro aroma is created by a half-dozen or so substances, and most of these are modified fragments of fat molecules called aldehydes. The same or similar aldehydes are also found in soaps and lotions and the bug family of insects.
In other words: BECAUSE IT IS SOAP. Green, evil soap.