To the OP. Everywhere you go? Perhaps you frequent the wrong places too often.
Also, some people use the term “off the derech” a bit too loosely. This past shabbos I heard a chassidishe yid use the term in reference to his son who married a litvishe girl and is a full fledged shmoer torah umitzvos, just on a path that is different than his father. Yes, he is off his fathers derech, but not off THE derech. Is this what our OP might mean?
Why someone might abandon torah and mitzvos is ultimately because torah umitzvos mean nothing to him/her. There are as many reasons as their are people why they find no meaning in torah and mitzvos (just as there is surely a reason this chassidishe fellow turned to a litvishe derech instead of the one he grew up on).