I wouldn’t label it as a “trend”, but I do believe there are people out there in their teens to early 20’s who are “exploring” their sexuality, and might be labeling themselves as “asexual”, when in fact they are still undergoing a transition to something more in keeping with what their desires are, or are afraid of experimentation; all sorts of reasons….
When we are older, we are more comfortable with our true selves and accept ourselves for who and what we are.