First, the orgasm, male or female, is hugely a mental thing. If your mind is elsewhere, or anything, it might not happen. Breathing and focusing in the pleasure/sensations. Too often a gut might worry about "her" and "her pleasure", which is worse than thinking about your mother, sister, baseball, etc. As mentioned, fake orgasms from the "pros" can make things better for some guys and worse for others.
If the ladies are having orgasms (sounds like this might be a civvie thing), as we know, many ladies cannot handle direct stimulation (oral or penetration) after they have an orgasm. Again, as with any relationship, even the sex requires communication and negotiation and compromises from time to time.
Not so obvious physical issues. Check with a plumbing doctor.
Other physical issues such as medications (anti-depressants, sleep aids, allergy meds, etc) can desensitize. Also, in P4P, if the lady really isn't into it, lube can be an issue. For me, if she isn't nice and wet (natural or otherwise) it is worse than trying to jerk off with my non-dominant hand. I was having a great session a little while ago and she was getting dry, and I didn't realize what the issue was at first as I was trying too hard to make it happen.
However, based on your second post, I am leaning towards mental/emotional factors getting in the way. Also, communicating what works for him to the lady. Maybe he felt comfortable enough with you to have his own pleasure, or your MO played into what he likes.
Some guys like/need a slow build the whole way. For me, slow is OK, but eventually I want things fast/intense to finish off. It is easy for an interruption in the rhythm to cause a major setback in progress, as well.
He needs to communicate this up front and work out solutions with a good/patient provider/lady. She needs to find a comfortable position that will work in the long haul, so that she can continue for the duration as needed. Usually it's the other way around, but he may need lot's of foreplay so that they are in the same general ballpark.
Too often we let the stereotypes of the sexes rule our actions. Even when these stereotypes are based on our youth (guys get hard thinking of pussy and ladies need all the foreplay), and the reality is that later in life the ladies are more sexual and the men less so (in general).