Because, you see, unlike the love between family and children, these two adults make a conscious decision to be together every day. Or, at least, they should. It's no wonder that marriages fall apart; that lovers leave; the feelings fade. Who can constantly decide that they want to breathe air or drink water? After being together for a while, for some people "a while" could be two days or two lifetimes, but whenever that period comes, people get comfortable. They get lazy. Somewhere along the way the love can turn to familial love, which is not to say that it doesn't work or that people can't be happy that way.
But it's not for me.
I'm not a great romantic. I don't like forced romantic gestures like door opening or beds of roses. But I do like choice. An adult decision to be together and accept that we choose to be together - not because it's easy or familiar or comfortable - but because we want the other one around. We want feeties in the bed, ticklish necks, hair on the shower wall, water bottles on the floor, socks everywhere, eggs and bacon in the morning, a sink full of dishes, a bed full of pillows, lots of hugs, lots of kisses, lots of I love yous, lots of fights, silliness, sadness, and love.