Walmart? You mean Temu and Etsy. Walmart doesn't ship their inventory piecemeal through the post.
But yes, the Etsy stuff is often sent piecemeal via Post.
What feels really gross is that they could ship a trinket from China to your door for less money than it would cost me to send it to someone in my own state.
Or some other courier or with a USPS postmark? Because that would indicate it got commercially brokered with all duties assessed and paid by someone.
Most small trinkets use something called ePacket, check its pricing here - https://jingsourcing.com/shipping-from-china-to-us-cost/
It would cost me as an American 4x that amount to send something to even my neighbor via USPS.
I wouldn't say I'm a tariff fan, but US sellers have been getting ripped off for years, and few people even know or care.