I can understand grouping shipping to cut costs, but not sure that answers my question fully.
The question still remains, why so many at once? He mentioned he had another shipment of ~90lbs on the way.
And I've seen similar purchases posted here from people that aren't overseas, so that explanation would not be relevant for people Stateside.
I've saved piles of money with flat rate international boxes, especially since my forwarder can fit 10 lbs of **** in a 5lb box!! (thanks WP!

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A lot of US eBay sellers ship domestically for free or for very little cost. As soon as they have to ship to Canada, for example, that cost doubles or triples and now with the wonderful Global Shipping program, you pay the customs plus other fees right up front (usually a lot more than actual customs would charge, if at all)...for one item. If I can fit 10-12 items into one flat rate international box, I pay ~$50 shipping one time, not 12 times.
I'm unsure if this applies to the person you were asking about (by the looks of his reply, it does on both counts) but sometimes people have to use alternate routes to get stuff they can't get locally or to get stuff at a more reasonable cost.