All these assertions that titanic did well on the back of some random teenage girls seeing it a few times is underselling it a tad.
Movies only gross even a third the numbers titanic did by being reasonable and engaging to watch for a huge number of people. Titanic therefore must be reasonable and engaging to a vast number.
It was certainly watchable, had some twists in the plot, ended in a reasonable way when she died, the SFX were spectacular, and must have obviously pressed the right buttons.
some math, if 5,000,000 girls saw it three times each @ $10 / time it's still only $150M, therefore the other $450M came from somewhere else. From this we can deduce that a lot of people saw this movie.