You know why they can't most of the time though? Girls don't properly communicate to their partners about what they want, where to go, deeper/harder, etc.
I don't struggle with this. Obviously clit stimulation is a good key to it and my man always goes down on me and makes me orgasm that way before PIV, but I still manage to orgasm with PIV because I TELL HIM WHAT I WANT HIM TO DO, AND HE DOES IT. If I want it harder, he goes harder. Cum time. Easy.
People just don't communicate during sex, and girls are actually fucking awful because they consistently lie or agree when a man is like "do you like this?" so don't give me your shit. I'm with this dude.