I think ZD has it on the money or the mark (or whatever the expression is). I used to be involved with one of these organizations, and I know that it is quite common for someone to sign up in a moment of inspiration or something else and to lose interest a moment later. This is especially true amongst the teenagers and college-aged students. Sometimes, it can also just be a bad “shidduch” and the student doesn’t know how to tell you.
That is why there usually are staff members available to help with these issues and/or act as a go-between between you and the student. You should call this staff member as soon as possible and discuss the issue with you. They will probably contact the student to find out what is happening and/or try to find you a new student who is more interested and is a better match for you.