A good topic for discussion, and thank you for sharing. Not having spoken to my guys friends on these topics, I can't really say, however, I can share some feedback from the women I've conversed with, and my thoughts as this question has come up. Most of the women I've spoken to share your experience(s), and I imagine we can point to some form of inadequacy. If I had a little more time, I could word-smith a little better but that's what comes to mind. I don't share this behavior and without deeper thought, I'm unclear on what to suggest to help your partner move past this issue.
That said and my 2 cents. Of the conversations and experiences that I've had women, they're all a little different with respect to how easy or difficult it is for them to reach orgasm and none could from penetration alone, with any of their partners. That's not to say intercourse isn't pleasurable for them, it just doesn't hit all the right places, and in the right ways, and for the duration of time that they need. It's just how the female body is designed.
A quick google search on this topic, the average time it takes a woman to reach orgasm is in the neighborhood of 15 minutes. Some sooner and some much longer. A woman posted a very good link with information and thoughts on this topic, and I'll share if I can find it. She also shared the same experience(s) with her partners. As a whole, men should spend more time understanding what their partners need and to keep in mind that whatever worked for a past partner, may not work for the others. Whether a woman can reach orgasm in 2min or 30, it's all within the norm. I certainly don't mind the process of learning what my partner needs. 😃
Hold your ground and maybe research this topic together.