I think that, specifically for the UK government, they hugely underestimsted the impact that kids and uni students going back to school and uni would have.
I think that, specifically for the UK, the government assumed that the protections the schools and unis would put in place would be enough.
I think that, specifically for the UK, the UK government is run by a bunch of out-of-touch middle aged men and the occasional childless middle aged woman, and so as a group they *do* lack the common sense you might find from mothers and involved parents.
I suspect that other countries may be similarly run by middle aged men and childless middle aged woman.
I have evidence that the UK government underestimated the impact schools and unis going back would have, from radio interviews, newspaper articles and the destruction of track and trace in September.
I have no idea what your point is