Because those costs were incurred with the plan to recoup the cost from sales in the US, and (presumably) those people are bypassing the licensed sale/use; which ruins that plan.
Your question is really no different than asking why it's not legal for me photocopy books and ignore copyright.
The problem is they already took the money and basically broke it after the fact. Typically there’s all sorts of legal protections protecting against something like that.
Why should we as a society enable plans and business models that hinge on taking away consumer freedom to get the product from the most competitive supplier instead of the one who wants to milk an artificial monopoly?
It was my understanding that the company they bought it from didn't have the rights to sell it in the US. As such, there's no real difference between buying from them and buying from someone that stole it and sold it to you.
Now, you can argue that country-specific licenses shouldn't be allowed; but they currently are.
I think most people can see the obvious ethical difference between actually stealing something vs breaking an exploitative license like that, and react accordingly.
Your question is really no different than asking why it's not legal for me photocopy books and ignore copyright.