Could be because of the massive rip-offs coming from China-based sellers. Common scam is to price a product very low, then add $$$$ shipping fees. Many buyers only look at the price, not the shipping cost. "Free shipping" is predominant, and people who don't read fine print also don't look at shipping costs. Once they've committed to buying the item, they're shocked by the shipping costs (often several times the purchase price of the item).
That's just one scam that's become endemic among Chinese sellers.
The ban won't hurt them, though, because most of them have local (in-USA) sellers now, acting as shipping forwarders/order fulfillment.