Cynical me again...
I think in the rarified world of politics lockdowns were, initially, perceived as being usefully cheaper, quicker and more decisive than investing in hospital capacity, staffing, structure and equipment. (Of course none of these are true. But perception counts for a lot in politics and they were dealing with a rapidly unfolding situation from a nation not famed for its transparency and reliable data.)
The government has taken a gamble — and it really has been an ‘all life savings on red’ thing — that covid would be a one-off. Therefore spending billions to rapidly and majorly reconfigure hospitals around an illness that might naturally peter out in two years — like most pandemics do, apart from HIV — might have been viewed at the time as a waste of money. (Again, probably wrong. But — elected officials fail to think beyond election cycle shocker.)
Furthermore — and this is where the cynic in me truly comes out — there was an opportunity to try to rally the country behind the NHS, at a time when the acute effects of Brexit plus decades of government underfunding had the service properly on the ropes. Get people clapping and shitting rainbows and a lot of them start to forget about £350 million on the side of a bus. Get people focused on the people who work for the NHS and they start to forget about the fuck-ups who fund it.
There’s an axiom in politics: we must do something, this is something, so we must do this. Lockdowns happened to be the thing that everyone was talking about because China had done them, so that’s what everyone else did too.
It was a lot of desperation, combined with a bit of cynicism. I don’t believe anyone in politics believed it would actually ‘work’ (whatever that means, beyond a claimed intent of reducing strain on health services it was always kept pretty vague).