They can't, I live in the UK. I am free to let a few weeds grow in my garden as long as it doesn't get to a point its blocking the public footpath that goes along my house or blocking out the sun to neighbours.

America, land of the free.

where they invented nightmarish levels of bureaucracy regulating every aspect of human existence.

It takes awhile before they send those warnings. And some places don't care if it's weeds, just that the weeds are short.

You can always keep moderate care of the property: just not too much. Forests, for example, need to be tendered, and (unexpectedly) sometimes trees have to be cut — to make more space for animals to thrive (not just humans), to other plants to grow.