Because a competent country/government should plan ahead for shortages of any vital resource it depends on.
Until quite recently, “the US sticks its dick in the chainsaw” wasn’t a “within reason” scenario.
Reason dictates having redundancy in place. Having prepared scenarios for what to do. A lot of countries clearly don't have that and they are operating on the assumption that no major disruption is going to happen.
Depending on resources coming from historically unstable locations and not having plans to prepare for such instability is just foolish.
The UK doesn’t have a strategic oxygen reserve in case the atmosphere disappears.
It’s both implausible and not really something they can do much about.
Trump is that sort of scenario.