Even in the modern era the cost is still relevant. Bricks are still pretty expensive.

If I have 100 acres (square), I need ~2.5 km of wall, at ~150,000 bricks for a 1m wall single brick-width wall (deter animals, mark property).

At the online prices I'm seeing ($0.65), that's ~$100,000. If I have to make it all double width, suddenly its $200,000. $100,000 delta is still pretty relevant for a modern small scale farmer.

wire dates to ancient sumeria i think; it was used for money before coins (because it's easy to measure out any desired amount of gold or silver)

I think that’s typically a job for fences, right?

This sort of wall is, I think, just an aesthetic way of marking a property line/get some privacy.

They were also dirt poor by current standards after industrialism started. It was well into the 19th century that laws like the Education Act of 1870 and the Trade Union Act of 1871 started distributing power to the common people of Britain outside of the traditional quasi-feudal system.