But here's the thing I've learned fairly recently: A lot of peeps didn't grow up with any sort of etiquette drilled into them. Because of this, they do what they want and whatever sounds like fun.
So, I've been to second showers, and I've been to showers hosted by the MTB. I've been because it would have been socially more awkward for me *not* to have gone to those particular showers.
I honestly just don't think people really think before they plan things, "Will this be tacky/rude/gift-grabby?" They just do what they want and what works for them.