Because just getting on top doesn't magically give you orgasmsMore
Lots of women have their most reliable orgasms by leaning back and rubbing, circling, or tapping their clits. If this is you, then do that. Hop on a bar stool (or dresser or table) and spread your legs. The positioning gives you free rein to rub yourself as you please. This makes his thrusts inside you feel extra amazing, plus he gets to watch exactly how you like to be touched.
Lie on your back with him flat on top of you, then straighten your legs and press them together with his legs on the outside. Roll your hips slowly and take ... your ... time. When one or both of you feels close, stop. Kiss, stroke his back, stare into his eyes, whatever stops the momentum. Repeat 'til you both are dying to finish — the point is to get so turned on that even if your clit is not being stroked in exactly the way you like it, orgasm is beyond inevitable.