What am I missing?

[m.flag5]

I recently bought 2 of the same products from 2 different ebay stores same price. I paid for both items immediately. Next day seller emails me and tells me to cancel 1 order because their computer didn’t update to show correct stock inventory because they own both of the stores. Why didn’t they just cancel the order on their end? 

[eburtonlab]

If the seller cancels as "out of stock" the seller's account receives a costly defect.

That is not the case if the buyer requests a cancellation.