I think in most cases they are picking up for friends or fellow board members.
In some cases, duplicates are for kitbashing or customs they might have planned.
Some folks buy 2 in order to keep one mint in package and take one out for display or play. I've seem folks on TFW who buy 3 - one to keep in package, one to display in bot mode, one to display in alt mode.
Sometimes they might have gotten a really good deal on multiples and be looking to use the duplicates for trades or resale.
Personally, I don't even buy repaints or minor remolds... but that's just me.
