1.
The common belief is that sex between couples gets TOO familiar and things can get stale and boring. What isn’t talked about as much is, you’re having sex with someone who knows your body backwards and forwards. (and maybe upside down) There’s no ramp-up period, no awkward or painful learning curve. When it’s time to get down, they already know where all your buttons are and they know exactly how to push them.
2.
Now we all know telling a sexual partner EXACTLY what you need isn’t always easy. You don’t want to hurt their feelings or make them feel as if they’re doing something wrong. However in a long term relationship with someone you trust, you will have much less hesitation to tell them “No, not like that… like THIS.”
I mean sure, there can be some awkwardness in admitting that you’d prefer to change up your established sexual routine, but, again, when you’ve been together for a while you’re more likely to have this met with acceptance and enthusiasm rather than judgement.