Mostly because other countries have culture, size, and other issues that make direct comparisons between say, the US and the UK or Mexico not very helpful. The US is as large as Europe. Comparing most European countries to US states makes more sense to me, and even then we have individual states.
I agree ... which may seem contradictory with my previous statement. However, since Valentina mentioned a need for verifiable data, I'm curious as to why it would be seen as inconsesquential. If they have data, then let's take a look at it and see if it fits with the US.
As you pointed out, such solutions are unlikely to be a good fit for the US. Texas is roughly three times the size of the UK with roughly 1/3 the population. Trying to use a UK solution in Texas is unlikely to function in the same way. Not to mention that you still have 49 other
states to deal with.
EDIT: the word "other" seemed important.