I'm no industry insider or anything, but I'm pretty sure the reason why you don't see many of either being made anymore is because of costs. With a blowbang, the male talent has got to be extremely costly and I'd assume that it doesn't really pay that well for the pornstar since she's probably only getting paid the "blowjob rate." And I'm sure a gangbang is even more costly because that pornstar is getting paid to do so much more (anal, DP, etc.); not to mention that pornstars often have to take a couple weeks off afterwards because of the intense pounding.
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