6. We both think the other person is sexy and treat them that way.
This reason should not be notable. But I suppose it must be, after I compared how my wife and I behave with the statistics about how often married people do Married People Stuff ™ in bed.
Throughout the day, whenever we are together, we pay attention to each other in ways that communicate "you are sexy". This happens with eye contact and little touches when we walk past one another. We like to sit close to each other. We sneak hugs and kisses when the kids are not looking (and often when they are). We purposefully keeping up our appearance at home and compliment each other on how we appreciate seeing our spouse in nicer clothes than sweatpants and a formless tee shirt. There is also the trick of paying
attention to the other person when they are not expecting it: this is the time a comment on how we are attracted to the other person's body seems most genuine. And of course there is lots of cuddling and Married People Stuff ™.