[78-L] Help me understand the logic...

[Benno Häupl]

. 
That's to avoid 'feedback bombing'. 
Unhappy customers used to buy many lots from their 'enemy seller' and were able to leave plenty of negative 
feedback and low DSR stars, thus ruining the seller's reputation and - especially - the 20% discount for eBay fees. 

Your seller has got nothing to do with it. It's a new default setting. Sellers can change these preferences in 'My eBay'. 

Benno 
.