It’s a very easy movie, almost guaranteed to work, and makes them money. I don’t know why they’re not doing it.

Probably because export tariffs make your product less appealing to import compared to other potential competing exporters who don’t collude on an export tax, or the target country who might be incentives to produce domestically instead of importing. Obviously, some industries are more geographically locked than others, but these deals still have knock on effects.