Congratulations, you've found fashion. The reason why things were more varied in previous generations is the speed of communications. it took much longer for fashions to permeate through society, this mean that more local variations happened. Now, fashions are almost always global, but they still change at the same rate. The difference being is that they change much more in unison across the globe.
Who cares if movie posters and book titles are converging towards something that markets well? The parts that matter (the content, themes, style, etc) are probably very different among all those books/movies.
IMO Fashion like this exists just so that salesmen can convince consumers that they can buy The Current Thing and earn respect from their peers. Chasing the latest furniture, latest clothes, latest cars, etc.. It's all a shallow, costly signal of wealth that excludes the not-wealthy and distracts the wealthy from more fulfilling/productive pursuits.
If this trend means that fashion is dying, good riddance.