When people decide to throw these horribly expensive weddings, some cost over $40K, I can see why others would bow out of being best men or bridesmaids.
My observation is that wedding customs in the US are silly and expensive beyond belief, and they more planned by an official planner they are, the more expensive and silly they are.
These women have done their best to make dumb shit rituals into American customs: the groom must remove the bride's garter with his teeth: the couple must mush wedding cake into one anothers' faces. The few formal weddings I have attended were dumber than Letterman's Stupid Pet Tricks. And every one of these expensive weddings ended in a nasty divorce within four years.
I would have missed them altogether, but my ex forced me to attend. We are divorced, but it was not a nasty one.