Here's the way I see it:
1. If I had sex with more than one woman at a time, 3 is the maximum number I can handle. 72 is just pointless. If i had sex with 3, what will the other 69 do? Just watch?
2. Why do they all have to be white girls? What about blacks, indians and latinos?
3. Not only are they white, but they are also translucent enough that you can see their bones. That's actually more of a turn-off than a turn-on if you ask me.
4. This is Jannah after all, I can have anything I want, as many as I want. 72 women would be considered nothing.
5. They are virgins! I don't want to see blood every time I have sex, thank you very much.
6. What about the poor gays? Oh yeah, they can just wish for their virgins to turn into men!
7. There will also be little boys who have died as children, and children don't have any sexual desires! They can just give their virgins to the lesbians! But there are not many lesbians as they are a small portion of the human race, so the extra will go to the straight women, and they can wish for them to turn into men! EVERYBODY'S HAPPY!
I've got it figured out. There's a general theme of what's haram on earth is halal in heaven. Wine, extra-marital sex, etc. So obviously what happens is all the women turn into lesbians and help themselves to all the unattended virgins.
Devious, treacherous, murderous, neanderthal, sub-human of the West.