Just so you know you are on the Australian boards. ebay.com.au

eBay no doubt employ marketing teams and one of the tasks would be to target market.

So targetting accounts that don't buy to entice usage of eBay would make sense.

I have also noticed when I don't buy for a while I get vouchers.

Similarly with a friends account. When they haven't used their account for 6 months or more, vouchers start appearing.