And yet national leaders do phenomenally unpopular things all the time when they decide it's necessary. In this particular case it's mostly moot because none of the other impacted countries really has the capability to act regardless of popularity or lack thereof. Like the UK chose to spend all of their money on nationalized healthcare instead of the military. I don't mean that in a critical or negative way, on balance that might have been the right choice for them. But that choice does constrain their options in a crisis.
The UK spends a lower fraction of its GDP on health than the US (the US is an outlier because of its system).
The UK's NHS is not why it's not taking part in this mess.
Would it not be pretty counterproductive for other countries to assist the US in this case? That seems only likely to prolong / exacerbate the war. The US giving up would be much faster.
Whether it would be counterproductive or not depends on what those other countries are trying to produce. None of them particularly want to pay tribute or protection money to Iran, especially because Iran could then decide to close the strait again or raise the fee at any time. They also don't want to set a precedent that other countries might exploit for charging transit fees through their national waters. And the USA might impose secondary sanctions on any country which makes payments to Iran. So the current stalemate might last quite a while.
"Like the UK chose to spend all of their money on nationalized healthcare instead of the military"
I believe the equation is a bit more complex than that.
Fair enough. There are a multiple additional reasons why the UK can no longer afford an expeditionary military to protect their overseas interests, but the full explanation can't fit into an HN comment. The exact reasons aren't relevant to the current state of affairs, the main point is that they lack the capability to do anything even if they wanted to.