Sellers marking shipped but still nothing

Ordered an item back on Jan 14th. Was marked as shipped the same day but tracking shows that usps is still waiting on the item. Have contacted the seller and gotten no response. Filing item not received today since estimated delivery was the 23rd. Why do sellers mark items shipped and even provide tracking if they never plan on shipping anything? This is getting annoying as it's happened to me multiple times in the past year. Some items I have received and others I never did and had to file a case to get my money back. On two occasions the sellers wouldn't mark it as shipped until I asked to cancel the order then miraculously they "already shipped it" and have tracking but in most cases they just get a tracking number and do nothing after that.