"So what has gone wrong here?"
Nothing, just really bad luck.
And a virus that can still take hold rapidly
There are rises in lots of places worldwide, whether nationally, regionally or smaller area, causing local restrictions. It's really important to learn how to spot small outbreaks and quash them, to prevent them linking up intoma more general rise.
Is it hard to see others having freedoms you don't - yes, and you can ask any of the shielded 2.5million. They were (and still,are) under closer restriction that everyone else, and even when deshielded, will still have fewer freedoms (in the sense that there will, unless advice is updated again, only be some out of the home activities that are OK'ed - essential shopping not all shopping, outdoor not indoor leisure etc).
And just like you, it protects them - but the reason the government did it was not concern for the individual but to stop the exceptionally medically vulnerable from filling all the NHS beds
(Nearby, but not inside the place zone)