Last time someone asked about this the reason I heard was that it's to prevent people from getting unsolicited messages asking them if they'll sell their item - same as what Zwouter said.

That definitely makes sense to me. If a user hasn't posted an item for sale on the market or market board then they probably don't want to sell it. If this is implemented maybe make it an opt out system? Users who don't care will have their names published on the lists. Users who'd rather not take part can turn off the option.