Tell me why!

I really do not understand......
Why do people bid and win an item and then not pay?
A lot of sellers block bidders with 0-3 feedback. I never did - after all, these people need to start somewhere and overall they have been great! They want to bid and buy things on ebay and they start building up their feedback.
In the last week I have been burned twice - Hermes men's sweater - $2200 went for $400 (sounds like a good deal to me) - buyer had 1 feedback. Nope - he didn't pay, didn't contact me, didn't respond to my emails. Chanel handbag - $1305 (at least a $2500 bag) - yup - again!
WHY oh WHY? I really do not understand.
Why would anyone want to do this? Don't they have better things to do with their time?
It really messes things up. Even though I know that they are not going to pay I can't really relist the item until 10 days have passed. After 10 days I can file a non-payment charge - but not until then. How can you relist the item if the matter is not closed? I do get back the final value fee but not the original listing fee. Ebay's charges are high for items like these.
Ebay is really a great place. Yesterday I sold a really beautiful brand new red leather and alligator BALENCIAGA bag. The bag is going to Indonesia. Isn't that great? I think so - my son-in-law thinks that I feel that I am doing a fashion service by moving these great things around (I don't know if he thinks that a $1600 bag is great). Well, I am! The bag was purchased in Paris - the gal who bought it never used it - and now it is going to someone who will love it who is in Indonesia. That's GREAT! and FUN!
Ebay can be a great place to do your shopping. Why do people have to try to ruin it? And they have succeeded! Yesterday I added a block to block buyers with less than 3 feedback. OK - they won! It really makes me angry.....