Feedback is NOT mandatory.

Many choose not to leave it these days.

Some have found out by asking for it that they might get what they do not like in their feedback.

Then there is old who should leave it first debate as well.

Buyers believe it should be left after they have paid and a lot of sellers do it after it has been left for them as they say the transaction is complete after the buyers leave it for the seller.

Some sellers leave it weekly and some monthly some have it auto set to go when it has been left for them and some not at all, as feedback for buyers means nothing when sellers are prevented from leaving honest factual feedback that ebay say should be left.