They have 'opened up' for Christmas because a lot of people would have ignored the rules and visited family anyway. This way stops the need for the army and police to be seen to be on the streets breaking up family gatherings as masses of people break the law.
Nobody wants to give their elderly parents or grandparents coronavirus.
Some of us have been working from home and have not left the house apart from a weekly shop. DS has come home from Uni, had two negative tests and not been out apart from an occasional late night run.
If DD was in the same position as DS we would have spent Christmas with DPs whatever the rules.
Unfortunately DD has only just finished school a week before Christmas so we won't.
My colleague has not been out since the summer and nor have her elderly parents. She will be spending Christmas with them whatever Boris says.
Let's just apply some common sense.