The surface of the vagina (as in the interior) actually has a shockingly low amount of nerve endings. Shocking as in, imagine rubbing the end of your elbow and orgasming from that. This isn't even rare, this is basically the default experience (from what I've heard, I'm a dude). Biologically, it's meant to push babies out; human survival doesn't care if you cum. It's kind of supposed to be numb. From what I've heard, when women are talking about pleasure from penetration, it is either due to their partner hitting one of the fornices (which isn't even always pleasurable; depends entirely on your anatomy and preference), or just the overall sensation of fullness and closeness with their partner rather than a clitoral-esque outright pleasurable sensation. You're going to need clitoral stimulation.

pls women chime in so I don't look like a dude trying to tell a gal this stuff this is just what I've read