This is why it was spreading so much when household mixing was allowed. Social distancing should have been happening, and if 2m not possible, then yes, masks should be worn in the home when other people are there.
I have been having to visit my elderly Mum during lockdown as she has a fall and broke her wrist, so needed help. We both wore masks.
I had a plumbing emergency during lockdown (water through the ceiling, and the plumber wore a mask - I thought it only fair to him to wear one too.