Because when we fall, we do it unknowingly, with the air current, along with the gravity, and without exerting any effort just like in love. When someone falls in love he/she does not have to put any effort to love someone, at least initially.

I  am really interested in Human hormones so I was reading this article which says that initially the love kind of resembles infatuations and the brain releases the hormones associated with anxiety, like cortisol. And identify the situation initially as a crisis. Later it releases dopamine which causes a feeling of happiness and oxytocin(main hormone releases after birth) which causes a sense of closeness. At that time we can definitely say that we rise in love after a brief moment of falling.

Rising in love is the same as not feeling love anymore. Take for example my very personal experience in love, which I'm ready to share:

I, once, fall in love with chocolate cookies but rose from that only to fall in love with wafer rolls (the ones that are filled with chocolate. Clarified that to not be misunderstood). Now, what I believe is important is not falling or rising but staying faithful, as the opposite of what I did with cookies.

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