My least favourite part of driving in the UK is that a road like this[1] (chosen at random from rural roads) has a speed-limit of 60mph/95kmh 0: https://www.google.com/maps/@51.358056,-2.6822578,3a,75y,344...
That's the default. These were introduced in the 1950s - before then, there was no national speed limit.
Councils and highway agencies can then decide due to a number of factors to reduce that number to what they deem appropriate. Most councils pull that down to 40mph in unpopulated areas, 30mph in built-up areas. Some councils - and the whole of Wales - pulled the built-up limit down to 20mph.
The Highways Agency has deemed some parts of the motorway network aren't safe at 70mph, so will drop the speed appropriately. Sometimes permanently (50mph on junctions is common), sometimes dynamically (overhead gantrys). It's all fine.
This is how the UK works - you set a default, and then let councils figure out things for themselves.
What you seem to be missing is that this is not a speed target. In most of the UK (notable exceptions include Greater Manchester and Hull, in my experience), drivers do not aim to get to that speed, they use their judgement.
On that road, there is no way much over 30mph is safe, as you don't have line of sight to oncoming traffic within a stopping distance. Do you know how I know that? The driving lessons and tests I took are far, far better than most in the World, even those my parents took.
Nobody is driving that road at 60mph without a death wish, but it doesn't mean we need to spend thousands of pounds per mile dropping the limit and then struggling to actually enforce it.