Why would the governments in these places be more interested in stealing bitcoin mining hardware than they are on taxing the earnings?
They are stealing it for themselves, for their own personal needs and use. And taxes go to the country's budget.
It would seem to make more sense to seize these items at the border with customs or some enforcement agency.
You can't do that because the border is too big, there are hundreds of smugglers.
Don't try to understand it, it's a completely different world.