Not having a vaginal orgasm is not uncommon - if I accurately recall the multiple surveys (scientific and otherwise) that I've read on the subject. So, I would assert that not being able to experience, in fact, does not make you defective. If that were the case - a large swath of the femail population would be as well.
I don't recall the specifics. But, in my own experience, it's only about 1/2 of the women I've been with are regularly able to have vaginal orgasms without alternative stimulation. For each it's different. For some, maybe a 1/3 of those who don't, I'm regularly successful with manual stimulation while having intercourse. But, it's not nearly an always thing. With many of the others, it's a real crapshoot. But, I have been fairly successful of getting them to orgasm prior to or immediately after vaginal intercourse.
Because I can typically engage in vaginal intercourse for extended periods of time, it's never been an issue of not having enough time for her to get there. I suppose it still could be the motion itself - but, when given, I take direction very well. Because of finding it frequently the case that many women don't easily orgasm vaginally without aid, i've never felt it to be anything but fairly normal outcome based on the structure of women's anatomy.
But, to your point of why have sex if you don't orgasm. I believe that there is something special about having vaginal intercourse. But, I view it as one of a number of exciting intimate activities I love to engage in. It matters not to me exactly where my member happens to be when climax occurs. But, I would guess that's a common sentiment for a guy
For some women, it seems that there's an over-investment (emotionally) in being able to climax via penis insertion alone. Not being a woman, I'm not sure I understand it.