"Trendy and fashion is for people who have no sense of style."
Running after trends - unless the trend in question is very healthy or practical which a trend usually isn't - seems to be for people who have no sense of what is their thing.
A sense of personal style usually comes with years and mistakes made. Probably all of us have made more or less successful tries at finding our thing and bags are a part of this. When someone unsure of their style sees a bag (or anything else that's trendy) that everyone wants or has, it'll be easy to convince yourself that you need to have that bag. They may know the bag is really expensive or overpriced, heavy, impractical etc, but they still have to try it.
Some people actually find their thing doing this. Lucky for them! For others, going along with trends usually is just an expensive way to find the style they're searching for.