Because that's reacting in surprise to an expected inevitable thing (infatuation fading), and presumably afterwards trying again with a different partner with a

Because that's reacting in surprise to an expected inevitable thing (infatuation fading), and presumably afterwards trying again with a different partner with an unrealistic expectation that in those relationships they might permanently stay "in love" i.e. the infatuated feeling of falling in love, which is quite distinct from long term relationships that we call "love" but IMHO don't apply the label of "fallen in love" anymore. In this case, if reality doesn't meet expectations, then divorcing just to try the same thing again to get the same result is absurd insanity, instead the expectations should be adjusted.