I've dated women like that.  They love sex and they loved having sex with me, but the only way they were going to have an orgasm was either with a vibrator, or by playing with their clit while I was inside them.

It's not a reflection on anybody's skills or lack of same (at least usually) but rather they're just doing what they need to do to have an orgasm.  One GF told me she masturbated with a heavy vibrator (the type you plug in the wall) and it desensitized her to the point of only being able to cum that way.

Once I finally talked to them about it and realized not to take it personally, I just told them to play away while I fucked them for all I was worth.  Since some women feel a little self-conscious about playing with their clit while you're inside them, I've learned to encourage them to do whatever it takes to get off. The orgasms started flowing and everyone went home happy.