No doubt, but Amazon communicates it to the consumer as $14.99 "with free shipping". To the consumer who habitually shops on Amazon and doesn't realize their dollar store sells it for $3.99, this sends the message that "$14.99 is just how much garden stakes cost these days, so I may as well buy them from Amazon who will ship them for free". If Amazon listed them for $3.99 with $11 shipping, it's the same total expense, but it would transparently signal to the consumer that the item itself ought to be cheaply available nearby if they get up and look for it.

Amazon doesn't want that thought to interrupt the 1-click checkout flow. And it apparently works; enough people seem to have internalized the idea that everything costs at least $15-$20 that they don't question it anymore. Soon your local dollar store is losing the economies of scale it used to have, cutting inventory and raising prices...