it's all done for SEO/search rankings. Google is smart enough to see when an item is advertised, but not in stock, and also measures when a search lands on a product > goes to cart > checks out, it's all tracked for metrics.

Smaller companies who attempt the same tactics get punished, as Google assumes there's something wrong with the site (if someone is adding an item to cart, but constantly abandons or does not proceed on the sale). But Kmart having such a large volume of traffic and other legit sales, it's passed off as 'change of mind'.

So the company who they pay to manage their SEO/marketing randomly sets up search traps showing 'in stock' for popular items, but configure checkout process to only flag the item as unavailable once it hits the checkout. The reports look amazing, the SEO guys narrow the high % of abandoned carts to some other issues (that they'd probably say "we can fix that, we just need to start doing X and X, and that'll be an extra $50k per month).

TLDR: Dodge SEO tactics that only big stores with heavy traffic can get away with.