People moved on to other movies because there are actually more then a few movies that are just as good or better then TFA currently playing in theaters. Titanic on the other hand had little to no competition quality wise for most of its theatrical run. I say it again besides Saving Private Ryan 1998 was a pretty lousy year quality wise.
Here are the 50 highest rated movies from 1998 on imdb:
Besides Saving Private Ryan and American History X pretty much all the movies on that list are pretty forgettable.
On top off all that 1998 was also a pretty lousy year music wise.
http://digitaldreamdoor.com/pages/bg_hits/bg_hits_98.html
Havent listed to any of those songs in a long time.