Another place I was surprised to see this was at UCLA. Busses of Japanese tourists stopping by to stroll the campus and shop in Ackerman (the student union). I don't see it as much anymore. In the '80s and early '90s, the department signs ("clothing," "stationery") were printed in Japanese and Chinese, as well as English.
Two reasons jump out at me for this kind of bulk shopping, be it LV purses or UCLA sweatshirts: 1. omiyage
. Japanese travellers bring back souvenirs for all of their close friends and relatives, which adds up to a lot of purchases, especially things like the UCLA sweatshirts that are not tremendously expensive and have brand recognition back in Japan. 2. Purchases for friends. I don't think it is uncommon (in any culture) to ask a friend going overseas to buy things for you (provided you pay them back). I've asked people heading to Japan to buy me particular electronics, people heading to Singapore to buy me watches, etc. This is actually the most likely source of any "resale" intentions, as I can easily picture an OL buying a bunch of bags then selling them to coworkers at cost or cost plus a token markup.