None of those countries ban companies from other countries they are at peace with from ownership of land containing mineral reserves, which is the policy that was suggested.
edit - one of the consequences of which would be foreign investors hiding the existence of useful minerals on any land they own and are using for something else, so it doesn't get taken away from them.
For minerals and energy, it's usually not done by restricting ownership of the land itself, but by retaining at least some mineral rights in state hands (or at least managed under a different legal regime). For example, the Norwegian state owns Norway's oil and gas reserves (originally outright, now via the partially privatized company Statoil). Anyone can buy land in Norway, but it doesn't come with ownership of oil/gas reserves.
Separating ownership of surface rights and mineral rights is fairly common in the U.S. as well, it's just that it's usually another private company that retains the mineral rights, not a publicly owned company. For example, the house I grew up in in Indiana did not come with ownership of mineral rights. The company that developed the subdivision sold us surface rights to the 1/4-acre lot our house was on, but retained the mineral rights underlying the entire subdivision (presumably just in case there turned out to be something there).
There is a massive difference between stopping all companies trading by enforcing national ownership of a resource and stopping foreigners trading resources that are legally on the market.
The question posed was not:
"Why are we selling something considered a national resource?"
It was:
"Why are we selling something considered a national resource to foreign owners?"
edit - also, I fully support mixed market economies with nationalised infrastructure, I think they seem to get more benevolent outcomes, but not with protectionist markets on the bits that are privately owned.
I agree with that, yeah (especially the last edit). I think the "national capitalism" approach, where things are privately owned but preferential access is given to important domestic corporations, often ends up mixing together the bad parts of public/private ownership rather than each of their good parts.
edit - one of the consequences of which would be foreign investors hiding the existence of useful minerals on any land they own and are using for something else, so it doesn't get taken away from them.