Good old-fashioned lust. Hylas was young and very good looking, and the nymph fell for him. As he was trying to get some water from her spring, she pulled him in and he was never seen again. read more
One of them says a nymph (possibly a different one from my last question) of the name was told by Hera to kidnap Hylas. On the Hylas page, it makes no mention of Dryope. read more