Lockdowns should work in theory and news reports suggest that they do help in the main but, they are defeated in part because not everyone adheres to them. I know this from casual observation in my own neighbourhood as some households have continued to meet and gather with others regardless. And I have never seen such frantic activity from builders and all sorts of trades in the neighbourhood since the pandemic began. No social distancing or masks whatsoever from these workers as I've seen.
On a better note, if the lockdowns are effective in constraining the virus at least to some degree then would they also not do the same with the usual winter flu bugs thereby easing to some degree the expected annual strain on the NHS? Serendipity springs to my mind with this but it never gets a mention in the news.