You talk of a lockdown - especially for hospitality - as if it is a trifling matter of little consequence. In the last week, because of various prophesies made by the "experts", hospitality venues have seen an avalanche of cancellations. Many of these places earn up to 40% of their annual profits in December, so they have been absolutely devastated. Most of them have yet to recover from last year's debacle and some have now packed it in for the rest of the year, unable to cope with this constant uncertainty. It's a fair bet that a number of them will never reopen.
In a normal year the hospitality industry contributes around £60bn to the UK economy and makes up about 3% of the country's turnover. As well as that it employs over 2.5m people, accounting for around 7% of the country's jobs. To glibly ask "why are the government dithering about so much?" is crass. It may be, because of the figures I quoted above, that the government is considering the matter carefully rather than simply locking the country down to protect the NHS from having to deal with a disease that is currently seeing about 5% of hospital beds occupied by its sufferers.
Of course there is nothing to prevent individual people and businesses from continuing to behave in the way you describe your parents' anniversary was conducted, nor indeed for businesses to close entirely if they are that much concerned. Personally I would hope they wouldn't. I went for a final meal of the year to my local family run Italian restaurant - Mum, Dad and daughter. I expected it to have suffered a wave of cancellations and to be empty. Fortunately I was wrong and it was packed (well as packed as it can be - they can only do 30 covers). I was pleased to see that some people had taken a pragmatic approach to the latest surge in infections and continued to behave relatively normally.