It might be that it is heat treated, and there could be some economics that make it importing it from the Baltics work. Maybe it is waste from lumbering and shipping could be cheaper than expected.
Across the country, there are a lot of regulations and restrictions at both state and federal level on moving non-heat-treated firewood. It looks like emerald ash bore, oak wilt, thousand cankers disease, and dutch elm are some of the main reasons for quarantines along with various local pests. Most of the firewood I see at the gas station, grocery store, etc is heat treated and comes from one of a few local "firewood factories" around here. It could be that it is easier at the distribution level in some places to just buy it in quantity from a wholesaler rather than try to find a local source, kind of like the 2x4s at the lumber yard come from the Pacific Northwest --more than a thousand miles from here-- even though we have lots of trees in MN that could be used.
And before anyone goes all "Nanny State! Nanny State!" these are plagues of trees, and states (and the feds) are trying to protect the economic assets of the forests the best they can. As woodworkers, we should support trying to protect our primary raw material. I'm not saying we should go buy imported firewood, especially if there is locally-sourced, legal firewood wood available.
Below is a link to a map giving the restrictions by state. Pretty much every state I clicked on had some kind of law on firewood movement.
https://www.dontmovefirewood.org/map/