Two factors contribute to these, both relating to the fact that Blue has been around a long time.
- Some people have lots of plat/items, and when they stop playing they decide to be generous and give them away
- Same as above, except some people like to "cash out" when they quit, and they use giveaways to cover up their (banned) RMT (this is mainly a concern for the buyer; the seller walks away with the cash even if the RMT gets caught)