Hi. I haven't read all of the replies (after it somehow drifted into gender politics, which I can get a month's supply of by accidentally watching  'The Drum')  so sorry if any of this has been covered.

First off, quite a lot of customers do leave feedback, but not quickly. I'm guilty of this myself. I know there are some items waiting feedback in my purchase history. I get feedback sometimes many weeks after the buyer received the item. 

All the same lots of people don't bother, and you just have to have a thick skin about it. It's not really rudeness, in the sense that unless they're sellers themselves, they probably see it as more of a courtesy than an expectation or obligation.

I do find that if you have any sort of contact with a buyer - even if it's just a note thanking them and letting them know the item has shipped - it increases the chance of  feedback. Don't ask me by how much; I haven't measured it.