Many would like to do as you have suggested and many do for the reason you highlighted, however I am just pointing out eBay policy. It is called Item Location, not Seller Location and is specific to where the item is being shipped from. The big issue is that if a customer in Sydney, lets say, buys an item that is described as being located in Sydney, finds that it takes 10-15 days to arrive and then in fact comes from China, they will more than likely be inclined to slam your feedback for being dishonest.
That's the best case scenario, if they report you to eBay, then you have them to worry about because of a listing violation.
Ultimately it's up to sellers what they list, but listing outside of eBay policy guidelines comes with violation consequences if eBay get onto you, and upset customers tend to get eBay involved pretty quickly .